#include<iostream> using namespace std; int main() { int n, m, s = 0, a[100][100]; cin >> n >> m; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { cin >> a[i][j]; } } for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { if (i+j==n-1||i==j){ s += a[i][j]; } } } cout << s; return 0; }