//%std
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
inline int read()
{
int out = 0, fh = 1;
char jp = getchar();
while ((jp > '9' || jp < '0') && jp != '-')
jp = getchar();
if (jp == '-')
fh = -1, jp = getchar();
while (jp >= '0' && jp <= '9')
out = out * 10 + jp - '0', jp = getchar();
return out * fh;
}
void print(int x)
{
if (x >= 10)
print(x / 10);
putchar('0' + x % 10);
}
void write(int x, char c)
{
if (x < 0)
putchar('-'), x = -x;
print(x);
putchar(c);
}
const int N = 40 + 10;
int n, m = 0, G[N][N], p[N], in[N];
double k;
void solve()
{
for (int i = 1; i <= n; ++i)
in[i] = 0;
int s = 0;
for (int i = 1; i <= n; ++i)
{
int f = 1;
for (int j = 1; j < i && f; ++j)
if (in[j] && !G[p[i]][p[j]])
f = 0;
if (f)
++s, in[i] = 1;
}
m = max(m, s);
}
int main()
{
n = read(), k = (double)(read());
for (int i = 1; i <= n; ++i)
for (int j = 1; j <= n; ++j)
G[i][j] = read();
iota(p + 1, p + n + 1, 1);
srand(time(0));
for (int i = 1; i <= 100000; ++i)
{
random_shuffle(p + 1, p + 1 + n);
solve();
}
double ans = (k / m) * (k / m) * m * (m - 1) / 2;
printf("%.7f\n", ans);
return 0;
}