#include <iostream>

using namespace std;

double sr(int[100][100], int, int);

int main()
{
    int a[100][100];
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
            cin >> a[i][j];
    double s = sr(a, n, m);
    cout << s << endl;

    return 0;
}

double sr(int a[100][100], int n, int m)
{
    double s = 0;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
            s += a[i][j];
    s /= n * m;
    return s;
}