ABC090A - Diagonal String

問題：A - Diagonal String

#include <iostream>
using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)

int main(void) {
    string c, ans = "";

    cin.tie(0);
    ios::sync_with_stdio(false);
    REP(i, 3) {
        cin >> c;
        ans += c[i];
    }

    cout << ans << "\n";
    return 0;
}