#include <bits/stdc++.h>
using namespace std;
int n;
int m;
string ans;
vector<vector<char>> board;
vector<vector<string>> dp;
string calc(int i, int j){
if(dp[i][j]!="-1") return dp[i][j];
dp[i][j] = board[i][j] + min(calc(i+1,j),calc(i,j+1));
return dp[i][j];
}
int main()
{
cin >> n >> m;
board = vector<vector<char>>(n,vector<char>(m));
dp = vector<vector<string>>(n,vector<string>(m, "-1"));
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
cin >> board[i][j];
}
}
dp[n-1][m-1] = board[n-1][m-1];
string s = "";
for(int j=m-1;j>=0;j--){
s=board[n-1][j]+s;
dp[n-1][j] = s;
}
s = "";
for(int i=n-1;i>=0;i--){
s=board[i][m-1]+s;
dp[i][m-1] = s;
}
cout << calc(0,0) << endl;
}
