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

using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<string> a;
    vector<vector<int>> count(m, vector<int>(30, 0));
    for (int i = 0; i < n; ++i) {
        string name;
        cin >> name;
        for (int j = 0; j < m; ++j) {
            count[j][name[j] - 'a']++;
        }
    }

    for(int i = 0; i < m; ++i) {
        char b = 'z';
        int c = 0;
        for (char a = 'a'; a <= 'z'; ++a) {
            int cur = count[i][a - 'a'];
            if (count[i][a - 'a'] >= c) {
                b = a;
                c = cur;
            }
        }
        cout << b;
    }
    cout << endl;
    return 0;
}