#include <iostream> using namespace std; int main() { int n, m, a[21][21] = {0}, sum1 = 0, sum2 = 0; cin >> n >> m; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { cin >> a[i][j]; sum1 += a[i][j]; if (i >= 1 && j >= 1 && i <= n - 2 && j <= m - 2) { sum2 += a[i][j]; } } } cout << sum1 - sum2; }