#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <set>
#include <random>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)

template<class T>
using vi = vector<T>;

template<class T>
using vii = vector<vi<T>>;

template<class T>
using viii = vector<vii<T>>;

int main()
{
    int h, w;
    cin >> h >> w;
    vi<string> s(h);
    rep(i, h) cin >> s[i];

    vi<string> dp(w);
    dp[0] = s[0][0];
    for (int j = 1; j < w; j++) dp[j] = dp[j - 1] + s[0][j];
    for(int i = 1; i < h; i++) {
        vi<string> prev(w);
        swap(prev, dp);
        dp[0] = prev[0] + s[i][0];
        for (int j = 1; j < w; j++) {
            dp[j] = dp[j - 1] + s[i][j];
            string temp = prev[j] + s[i][j];
            if (temp < dp[j]) dp[j] = temp;
        }
    }
    cout << dp[w - 1] << endl;
    return 0;
}