#include <memory.h>
#include <iomanip>
#include <cmath>
using namespace std;
#include <iostream>

int s[9][9]; // 给个各自的分数
int sum[9][9];  // （1,1）到（i,j）的矩形的分数之和
int res[15][9][9][9][9];

int calSum(int x1,int y1,int x2,int y2){//（x1，y1）到（x2，y2）的矩形的分数之和
    return sum[x2][y2]- sum[x2][y1-1] - sum[x1-1][y2] + sum[x1-1][y1-1];
}

int fun(int n,int x1,int y1,int x2, int y2){
    int t,a,b,c,e,MIN = 10000000;
    if(res[n][x1][y1][x2][y2]!=-1)
        return res[n][x1][y1][x2][y2];
    if(n==1){
        t = calSum(x1,y1,x2,y2);
        res[n][x1][y1][x2][y2] = t*t;
        return t*t;
    }
    for(a = x1;a<x2;a++){
        c = calSum(a+1,y1,x2,y2);
        e = calSum(x1,y1,a,y2);
        t = min(fun(n-1,x1,y1,a,y2)+ c*c, fun(n-1,a+1,y1,x2,y2)+e*e);
        if(MIN > t) MIN = t;
    }
    for(b = y1; b<y2; b++){
        c =calSum(x1,b+1,x2,y2);
        e = calSum(x1,y1,x2,b);
        t = min(fun(n-1,x1,y1,x2,b)+c*c,fun(n-1,x1,b+1,x2,y2)+e*e);
        if(MIN > t) MIN = t;
    }
    res[n][x1][y1][x2][y2] = MIN;
    return MIN;
}

int main(){
    memset(sum,0,sizeof(sum));
    memset(res,-1,sizeof(res));
    int n;
    cin>>n;
    for(int i = 1;i<9;i++){
        for(int j=1,rowsum=0;j<9;j++){
            cin>>s[i][j];
            rowsum +=s[i][j];
            sum[i][j] += sum[i-1][j] + rowsum;
        }
    }
    double result = n * fun(n,1,1,8,8)-sum[8][8]*sum[8][8];
    cout<<setiosflags(ios::fixed)<<setprecision(3)<<sqrt(result/(n*n))<<endl;
    return 0;

}