02. Primary Diagonal

#include <iostream>
#include <vector>

using namespace std;

int main() {
    int n, el;
    cin >> n;

    vector<vector<int>> matrix;

    for (int i = 0; i < n; i++) {
        vector<int> currentRow;
        for (int j = 0; j < n; j++) {
            cin >> el;
            currentRow.push_back(el);
        }
        matrix.push_back(currentRow);
    }

    int sum = 0;

    for (int i = 0; i < n; i++) {
        sum += matrix[i][i];
    }

    cout << sum << endl;
    return 0;
}