#include <vector>
#include <string>
#include <iostream>
#include <algorithm>

using namespace std;

int main() {
	int n,m;
	cin >> n >> m;
	vector<string> names(n);
	for(int i=0;i<n;i++) {
		cin >> names[i];
	}
	string country = "";
	for(int j=0; j<m; j++) {
		vector<size_t> count(26,0);
		for(int i=0; i<n; i++) {
			count[size_t(names[i][j]-'a')]++;
		}
		auto it = max_element(count.begin(), count.end());
		country += 'a' + char(distance(count.begin(), it));
	}
	cout << country << endl;
	return 0;
}