#include<cstdio>
#include<cstring>
#include<cmath>
#define MIN(x,y) ((x)>(y)?(y):(x))
#define INF 0x3f3f3f3f
using namespace std;
int N;
int map[10][10];
int dp[16][10][10][10][10];
int cal(int x1,int x2,int y1,int y2)
{
int ans=map[x2][y2]-map[x2][y1-1]-map[x1-1][y2]+map[x1-1][y1-1];
return ans*ans;
}
int dfs(int x1,int x2,int y1,int y2,int n)
{
if(dp[n][x1][x2][y1][y2]!=-1)
return dp[n][x1][x2][y1][y2];
if(n==N-1)
return dp[n][x1][x2][y1][y2]=cal(x1,x2,y1,y2);
int t=INF;
for(int k=x1;k<x2;k++)
{
t=MIN(t,dfs(x1,k,y1,y2,n+1)+cal(k+1,x2,y1,y2));
t=MIN(t,dfs(k+1,x2,y1,y2,n+1)+cal(x1,k,y1,y2));
}
for(int k=y1;k<y2;k++)
{
t=MIN(t,dfs(x1,x2,y1,k,n+1)+cal(x1,x2,k+1,y2));
t=MIN(t,dfs(x1,x2,k+1,y2,n+1)+cal(x1,x2,y1,k));
}
return dp[n][x1][x2][y1][y2]=t;
}
int main()
{
scanf("%d",&N);
memset(dp,-1,sizeof(dp));
memset(map,0,sizeof(map));
for(int i=1;i<=8;i++)
for(int j=1;j<=8;j++)
{
scanf("%d",&map[i][j]);
map[i][j]+=map[i-1][j]+map[i][j-1]-map[i-1][j-1];
}
double average=(double)map[8][8]/N;
printf("%.3f\n",sqrt(dfs(1,8,1,8,0)*1.0/N-average*average));
}
