#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2e3 + 5;
int n, m;
char mat[MAXN][MAXN];
string rijeci[MAXN][MAXN];
void popuni() {
for (int x = 0; x < n; x++) {
for (int y = 0; y < m; y++) {
if (!x && !y) {
rijeci[x][y] = mat[x][y];
continue;
}
string s = "z";
if (x) s = rijeci[x - 1][y];
if (y) s = min(s, rijeci[x][y - 1]);
rijeci[x][y] = s + mat[x][y];
}
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n >> m;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> mat[i][j];
}
}
popuni();
/*
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cout << rijeci[i][j] << " ";
}
cout << '\n';
}
*/
cout << rijeci[n - 1][m - 1];
return 0;
}
