#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	int n;
	cin >> n;
	vector<string> s(n);
	rep(i, n) cin >> s[i];
	string ans = "";
	rep(i, n) ans += s[i][i] == 'a' ? "b" : "a";
	cout << ans << endl;
	return 0;
}