// https://omegaup.com/arena/problem/Suma-de-la-diagonal
#include <stdio.h>

int main( ) {
   int n;
   scanf("%d", &n);

   int mat[n][n];
   for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) {
         scanf("%d", &mat[i][j]);
      }
   }

   int suma = 0;
   for (int i = 0; i < n; ++i) {
      suma += mat[i][i];
   }
   printf("%d", suma);
}