#include <iostream>
#include <math.h>
#include <string.h>
#include <algorithm>
#define INF 0x3f3f3f3f
using namespace std;
int n;
double dp[10][10][10][10][17];
int fen[9][9], sum[9][9];
double getxi2(int i1, int j1, int i2, int j2){
return pow(1.0*sum[i2][j2]-sum[i1-1][j2]-sum[i2][j1-1]+sum[i1-1][j1-1], 2);
}
double mind(double a, double b){
return a < b ? a : b;
}
int main()
{
scanf("%d", &n);
for (int i = 1; i <= 8;i++)
for (int j = 1; j <= 8; j++)
scanf("%d", &fen[i][j]);
memset(sum, 0, sizeof sum);
memset(dp, 0, sizeof dp);
for (int i = 1; i <= 8;i++)
for (int j = 1; j <= 8; j++){
sum[i][j] = sum[i][j-1] + sum[i-1][j] - sum[i-1][j-1] + fen[i][j];
}
for (int i1 = 1; i1 <= 8;i1++)
for (int j1 = 1; j1 <= 8;j1++)
for (int i2 = i1; i2 <= 8;i2++)
for (int j2 = j1; j2 <= 8; j2++){
dp[i1][j1][i2][j2][0] = getxi2(i1, j1, i2, j2);
}
for (int i = 1; i <= n-1; i++)//I表示 切i 刀;
for (int i1 = 1; i1 <= 8; i1++)
for (int j1 = 1; j1 <= 8; j1++)
for (int i2 = i1; i2 <= 8; i2++)
for (int j2 = j1; j2 <= 8; j2++){
dp[i1][j1][i2][j2][i] = INF;
for (int k = i1; k < i2; k++){//横切
dp[i1][j1][i2][j2][i] = mind(dp[i1][j1][i2][j2][i], mind(dp[i1][j1][k][j2][0] + dp[k + 1][j1][i2][j2][i - 1], dp[i1][j1][k][j2][i - 1] + dp[k+1][j1][i2][j2][0]));
}
for (int k = j1; k < j2; k++){//竖切
dp[i1][j1][i2][j2][i] = mind(dp[i1][j1][i2][j2][i], mind(dp[i1][j1][i2][k][0] + dp[i1][k + 1][i2][j2][i - 1], dp[i1][j1][i2][k][i - 1] + dp[i1][k + 1][i2][j2][0]));
}
}
printf("%.3lf", sqrt(dp[1][1][8][8][n-1]/n-pow(1.0*sum[8][8]/n,2)));
return 0;
}