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

int main() {
    int n, m;
    scanf("%d %d", &n, &m);
    pair<int,char> dp[n + 1][m + 1];
    string s;
    for (int i = 0; i < n; i++) {
        cin >> s;
        cin.ignore();
        for(int j = 0; j < m; j++)
            dp[i][j].second = s[j];
    }
    for (int i = 0; i <= m; i++) 
        dp[n][i] = {INT_MAX, 'z' + 1};
    for (int i = 0; i <= n; i++) 
        dp[i][m] = {INT_MAX, 'z' + 1};
    dp[n][m - 1].first = dp[n - 1][m].first = 0;
    for (int i = n - 1; i >= 0; i--)
        for (int j = m - 1; j >= 0; j--)
            dp[i][j].first = 1 + min(dp[i + 1][j].first, dp[i][j + 1].first);
    string ans = "";
    ans.push_back(dp[0][0].second);
    int i = 0,j = 0;
    while (i < n - 1 || j < m - 1) {
        if (dp[i][j + 1] < dp[i + 1][j]) {
            ans.push_back(dp[i][j + 1].second);
            j++;
        }
        else {
            ans.push_back(dp[i + 1][j].second);
            i++;
        }
    }
    cout << ans;
    return 0;
}