#include <cstdio>

#include <algorithm>

#include <cstring>

#include <cmath>

#define INF 0x3f3f3f3f

using namespace std;

int dp[10][10][10][10][16], sum[10][10][10][10];

bool v[10][10][10][10][16];

int a[10][10];

void init() {

	for (int l1 = 1; l1 <= 8; l1++)

		for (int r1 = 1; r1 <= 8; r1++)

			for (int l2 = l1; l2 <= 8; l2++)

				for (int r2 = r1; r2 <= 8; r2++) {

					int ans = 0;

					for (int i = l1; i <= l2; i++)

						for (int j = r1; j <= r2; j++) {

							ans += a[i][j];

						}

					sum[l1][r1][l2][r2] = ans * ans;

				}

}

int solve(int l1, int r1, int l2, int r2, int k) {

	if (v[l1][r1][l2][r2][k]) return dp[l1][r1][l2][r2][k];

	if (k == 1) {

		return dp[l1][r1][l2][r2][k] = sum[l1][r1][l2][r2];

	}

	int ans = INF;

	for (int i = l1; i < l2; i++) {

		ans = min(ans, min(solve(l1, r1, i, r2, k - 1) + sum[i + 1][r1][l2][r2], solve(i + 1, r1, l2, r2, k - 1) + sum[l1][r1][i][r2]));

	}

	for (int i = r1; i < r2; i++) {

		ans = min(ans, min(solve(l1, r1, l2, i, k - 1) + sum[l1][i + 1][l2][r2], solve(l1, i + 1, l2, r2, k - 1) + sum[l1][r1][l2][i]));

	}

	v[l1][r1][l2][r2][k] = 1;

	return dp[l1][r1][l2][r2][k] = ans;

}

int main() {

	int n, tot = 0;

	scanf("%d", &n);

	for (int i = 1; i <= 8; i ++) {

		for (int j = 1; j <= 8 ; j++) {

			scanf("%d", &a[i][j]);

			tot += a[i][j];

		}

	}

	init();

	solve(1, 1, 8, 8, n);

	double ans = sqrt(dp[1][1][8][8][n] * 1.0 / n - (tot * 1.0 / n) * (tot * 1.0 / n));

	printf("%.3f\n", ans);

}