#include<iostream>
#include<string>

using namespace std;

string A[1000];
int cnt[26];

int main() {
	int n, m;
	cin >> n >> m;
	for (int i=0; i<n; i++) cin >> A[i];
	for (int i=0; i<m; i++) {
		for (int j = 0; j < 26; j++) cnt[j] = 0;
		for (int j = 0; j < n; j++) cnt[A[j][i] - 'a']++;

		int k = 0;
		for (int j = 0; j < 26; j++) if (cnt[j] > cnt[k]) k = j;
		cout << (char)(k + 'a');
	}
	cout << endl;
	return 0;
}