import java.io.*;


class Main{
    static BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
    static int N = 15, M = 9;
    static double[][][][][] dp = new double[M][M][M][M][N];
    static double[][] s = new double[M][M];  //矩阵前缀和
    static double X, X2;
    static int n;
    static int INF = 0x3f3f3f3f;
    public static void main(String[] args) throws Exception{
        n = Integer.valueOf(read.readLine());
        for(int i = 1; i <= 8; i++){
            String[] ss = read.readLine().split(" +");
            for(int j = 1; j <= 8; j++){
                s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + Integer.valueOf(ss[j - 1]);
            }
        }

        X = s[8][8] / n;
        X2 = X * X;

        dfs(1, 1, 8, 8, n);
        System.out.println(String.format("%.3f",Math.sqrt(dp[1][1][8][8][n])));
    }

    public static double dfs(int x1, int y1, int x2, int y2, int k){
        double val = dp[x1][y1][x2][y2][k];
        if(val > 0) return val;
        if(k == 1)  {
            dp[x1][y1][x2][y2][k] = get(x1, y1, x2, y2);
            return dp[x1][y1][x2][y2][k];
        }
        double min = INF;

        //横切
        for(int i = x1; i < x2; i++){
            //上半部分
            min = Math.min(min, dfs(x1, y1, i, y2, k - 1) + get(i + 1, y1, x2, y2));
            //下半部分
            min = Math.min(min, dfs(i + 1, y1, x2, y2, k - 1) + get(x1, y1, i, y2));
        }

        //纵切
        for(int j = y1; j < y2; j++){
            min = Math.min(min, dfs(x1, y1, x2, j, k - 1) + get(x1, j + 1, x2, y2));
            min = Math.min(min, dfs(x1, j + 1, x2, y2, k - 1) + get(x1, y1, x2, j));
        }
        dp[x1][y1][x2][y2][k] = min;
        return min;
    }


    public static double get(int x1 , int y1 , int  x2 , int y2){
        double sum = s[x2][y2] - s[x2][y1-1] - s[x1-1][y2] + s[x1-1][y1-1] ;
        sum -= X ;

        return sum * sum / n ;
    }
}