#include <iostream>

#include <cstdio>

#include <algorithm>

#include <queue>

#include <vector>

#include <math.h>

#include <string.h>

#include <string>

#include <map>

#include<stack>

#include<set>

#include<string.h>

#include<iomanip>

#define pb push_back

#define _for(i, a, b) for (int i = (a); i<(b); ++i)

#define _rep(i, a, b) for (int i = (a); i <= (b); ++i)

using namespace std;

const  int N =+ ;

//double num[N], price[N], ave[N];

int s[N][N];

int sum[N][N];

int res[][N][N][N][N];

int calSum(int x1, int y1, int x2, int y2) {

    return sum[x2][y2] - sum[x2][y1-] - sum[x1-][y2] + sum[x1-][y1-];

}

int f(int n, int x1, int y1, int x2, int y2) {

    int t, a, b, c, e, mn = 1e7;

    int& ans = res[n][x1][y1][x2][y2];

    if (ans != -) return ans;

    if (n == ) {

        t = calSum(x1, y1, x2, y2);

        ans = t*t;

        return ans;

    }

    for (a = x1; a < x2; a++) {

        c = calSum(a + , y1, x2, y2);

        e = calSum(x1, y1, a, y2);

        t = min(c*c + f(n - , x1, y1, a, y2), e*e + f(n-,a + , y1, x2, y2));

        if (mn > t)mn = t;

    }

    for (b = y1; b < y2; b++) {

        c = calSum(x1, b+, x2, y2);

        e = calSum(x1, y1, x2, b);

        t = min(c*c + f(n-,x1, y1, x2, b), e*e + f(n-,x1, b + , x2, y2));

        if (mn > t)mn = t;

    }

    ans = mn;

    return ans;

}

int main() {

    memset(res, -, sizeof(res));

    int n;

    cin >> n;

    _for(i,,)

        for(int j=,rowsum=;j<;j++) {

        cin >> s[i][j];

        rowsum += s[i][j];

        sum[i][j] += sum[i - ][j] + rowsum;

    }

    double result = n*f(n, , , , ) - sum[][] * sum[][];

    cout << setiosflags(ios::fixed) << setprecision() << sqrt(result / (n*n)) << endl;

    system("pause");

}