I was learning about binary lifting and solving this problem on cses, it runs fine on smaller visualizable cases, but is failing on every large testcase. Can someone help?Link to problem

#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define all(a) a.begin(),a.end()
#define flash ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define test int t;cin>>t;while(t--)
#define loop(n) for(int i=0;i<n;i++)
#define input(arr,n) for(int i=0;i<n;i++)cin>>arr[i];
#define nline "\n"
#define P pair<ll,pair<ll,ll>>
using namespace std;
using namespace chrono;
int MOD=1000000007; 
bool valid(int x,int y,int n,int m){return x>=0 && x<n && y>=0 && y<m;}
int powMod(int a,int n){ ll ans=1;for(int i=1;i<=n;i++){ ans=(ans*a)%MOD;}return ans%MOD; }
vector<int>dx={0,0,1,-1};
vector<int>dy={1,-1,0,0};

class TreeAncestor {
  public:
  vector<vector<int>>up;
  int LOG;
  TreeAncestor(int n, vector<int>& parent) {
      LOG = ceil(log2(n));
      up.resize(n+1,vector<int>(LOG+1,-1));
      for(int i=0;i<=n;i++)
      {
          up[i][0]=parent[i];
      }   

      for(int j=1;j<=LOG;j++)
      {
          for(int i=0;i<=n;i++)
          {
              if(up[i][j-1]!=-1)
              up[i][j] = up[up[i][j-1]][j-1];
              else 
              up[i][j]=-1;
              
          }
      }
  }
    
  int getKthAncestor(int node, int k) {
   
      if(k==1)
      return up[node][0];

     
      int ans=node;
      for(int j=0;j<=LOG;j++) //O(log(N))
      {
          if(k&(1<<j))
          {
              ans=up[ans][j];
              if(ans==-1)
              break;

              k-=(1<<j);
          }
      }

      return ans;
  }
};


void solve()
{
  int n,q;
  cin>>n>>q;
  vector<int>parent(n+1);
  for(int i=1;i<=n;i++)
  {
    int u;
    cin>>u;
    parent[i]=u;
  }
  TreeAncestor ob(n,parent);

  for(int i=0;i<q;i++)
  {
    int node,k;
    cin>>node>>k;

    cout<<ob.getKthAncestor(node,k)<<nline;
  }


}
int main()
{
  flash
  auto start1 = high_resolution_clock::now();
  // test
  solve();
  auto stop1 = high_resolution_clock::now();
  auto duration = duration_cast<microseconds>(stop1 - start1);
  cerr << "Time in miliseconds: " << duration.count() / 1000 << endl;
  return 0;
}