#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define rep(i,a,b) for(auto i=(a); i<(b); ++i)
#define REP(i,n) rep(i,0,n)
#define all(v) (v).begin(), (v).end()
#define rs resize
#define DBG(x) cerr << __LINE__ << ": " << #x << " = " << (x) << endl

const ld PI = acos(-1.0);
template<class T> using min_queue =
priority_queue<T, vector<T>, greater<T>>;
template<class T> int sz(const T &x) {
    return (int) x.size(); // copy the ampersand(&)!
}

template<class T> ostream& operator<<(ostream &os, vector<T> &v) {
    os << "\n[";
    for(T &x : v) os << x << ',';
    return os << "]\n";
}

struct pairhash {
    public:
    template<typename T1, typename T2>
    size_t operator()(const pair<T1, T2> &p) const {
        size_t lhs = hash<T1>()(p.x);
        size_t rhs = hash<T2>()(p.y);
        return lhs ^ (rhs+0x9e3779b9+(lhs<<6)+(lhs>>2));
    }
};

void run() {
	ll n, m;
	cin >> n >> m;
	vector<string> A(n);
	for (ll i = 0; i < n; i++) {
		cin >> A[i];
	}
	for (ll i = 0; i < m; i++) {
		vi B(26, 0);
		for (string a : A) {
			B[a[i]-'a']++;
		}
		ll bs = -1;
		char bc;
		for (ll j = 0; j < 26; j++) {
			if (B[j] > bs) {
				bs = B[j];
				bc = 'a' + j;
			}
		}
		cout << bc;
	}
	cout << endl;
}

signed main() {
    // DON'T MIX "scanf" and "cin"!
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout << fixed << setprecision(20);
    run();
    return 0;
}