#include <bits/stdc++.h>
#include <string>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef double rl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

typedef pii int2;
typedef tuple<int, int, int>           int3;
typedef tuple<int, int, int, int>      int4;
typedef tuple<int, int, int, int, int> int5;

typedef pll ll2;
typedef tuple<ll, ll, ll>         ll3;
typedef tuple<ll, ll, ll, ll>     ll4;
typedef tuple<ll, ll, ll, ll, ll> ll5;

#define g0(x) get<0>(x)
#define g1(x) get<1>(x)
#define g2(x) get<2>(x)
#define g3(x) get<3>(x)
#define g4(x) get<4>(x)

typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<ll> vll;
typedef vector<pll> vll_ll;
typedef vector<vi> vvi;
typedef vector<vii> vvii;
typedef vector<vll> vvll;
typedef vector<vll_ll> vvll_ll;

#define pb push_back
#define mp make_pair
#define eb emplace_back
#define xx first
#define yy second

#define FOR(i,N) for(int i=0; i<N; i++)

//#define my_to_string to_string

template <typename A, typename B>
string my_to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string my_to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string my_to_string(tuple<A, B, C, D> p);

string my_to_string(const string& s) {
  return '"' + s + '"';
}

string my_to_string(const char* s) {
  return my_to_string((string) s);
}

string my_to_string(bool b) {
  return (b ? "true" : "false");
}

string my_to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += my_to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string my_to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

string my_to_string(uint8_t  a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(uint16_t a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(uint32_t a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(uint64_t a) { ostringstream ss; ss << a; return ss.str(); }

string my_to_string(int8_t   a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(int16_t  a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(int32_t  a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(int64_t  a) { ostringstream ss; ss << a; return ss.str(); }

string my_to_string(float       a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(     double a) { ostringstream ss; ss << a; return ss.str(); }
string my_to_string(long double a) { ostringstream ss; ss << a; return ss.str(); }

string my_to_string(         char a) { ostringstream ss; ss << '\'' << a << '\''; return ss.str(); }
//string my_to_string(unsigned char a) { ostringstream ss; ss << '\'' << a << '\''; return ss.str(); }

// anything that's a range (has .begin(), .end())
template <typename A>
string my_to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += my_to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string my_to_string(pair<A, B> p) {
  return "(" + my_to_string(p.first) + ", " + my_to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string my_to_string(tuple<A, B, C> p) {
  return "(" + my_to_string(get<0>(p)) + ", " + my_to_string(get<1>(p)) + ", " + my_to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string my_to_string(tuple<A, B, C, D> p) {
  return "(" + my_to_string(get<0>(p)) + ", " + my_to_string(get<1>(p)) + ", " + my_to_string(get<2>(p)) + ", " + my_to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << my_to_string(H);
  debug_out(T...);
}

#if !ONLINE_JUDGE && 0
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...) 42
#endif

int n;
const int MX=509;
int a[MX];

bool can1[MX][MX];
int result[MX];

int solve()
{
    //for(int i=0; i<n; i++) can1[i][i]=true;

    for(int L=0; L<n; L++)
    {
        for(int R=L; R<n; R++)
        {
            stack<int> S; S.push(a[L]);
            for(int i=L+1; i<=R; i++)
            {
                S.push(a[i]);

                while(S.size()>1)
                {
                    int bb=S.top(); S.pop();
                    int aa=S.top(); S.pop();
                    if(aa==bb)
                    {
                        S.push(aa+1);
                    }
                    else
                    {
                        S.push(aa);
                        S.push(bb);
                        break;
                    }
                }
            }

            can1[L][R]=(S.size()==1);
            if(can1[L][R])
            {
                dbg(L, R);
            }
        }
    }

    const int INF=1e5;
    for(int i=0; i<=n; i++) result[i]=INF;

    result[0]=0;

    for(int i=0; i<n; i++)
    {
        for(int j=i+1; j<=n; j++)
        {
            if(can1[i][j-1]) result[j]=min(result[j], result[i]+1);
        }
    }

    return result[n];

    //return -3;
}

int main()
{
#if !ONLINE_JUDGE && 0
    freopen("E.txt", "r", stdin);
    //freopen("output.txt", "w", stdout);
#endif
#if 0
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
#endif

    cin >> n;
    for(int i=0; i<n; i++) cin >> a[i];
    cout << solve();

    return 0;
}