#include <bits/stdc++.h>

using namespace std;

const int oo = 0x3f3f3f3f;
const double eps = 1e-9;
const double PI = 2.0 * acos(0.0);


typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<string> vs;

#define sz(c) int((c).size())
#define all(c) (c).begin(), (c).end()
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define FORS(i,a,b,s) for (int i = (a); i < (b); i=i+(s))
#define FORD(i,a,b) for (int i = int(b)-1; i >= (a); i--)
#define FORIT(i,c) for (__typeof__((c).begin()) i = (c).begin(); i != (c).end(); i++)

map<char,int> M[1000];

int main(){
	int n,m; cin >> n >> m;

	FOR(i,0,n){
		string s; cin >> s;
		FOR(j,0,m)
			M[j][s[j]]++;
	}

	FOR(j,0,m){
		char mm = 'a';
		FOR(i,0,26)
			if (M[j]['a' + i] > M[j][mm]) mm = 'a' + i;
		cout << mm;
	}

	cout << endl;
}