#include <bits/stdc++.h>
#define ll long long
#define F first
#define S second
#define pb push_back
using namespace std;
short n,m;
string s;
char c[2001][2001];
pair<short,short> dp[2001][2001];
void Rec(short i,short j)
{
s+=c[i][j];
if (i==0 && j==0)
return;
else Rec(dp[i][j].F,dp[i][j].S);
}
int main()
{
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> m;
for(short i=0;i<n;i++)
for(short j=0;j<m;j++) cin >> c[i][j];
dp[0][0]={0,0};
for(short i=0;i<n;i++)
for(short j=0;j<m;j++)
if (i-1>=0 && j-1>=0)
{
if (c[i][j]+c[i-1][j]<c[i][j]+c[i][j-1]) dp[i][j]={i-1,j};
else dp[i][j]={i,j-1};
}
else if (i-1>=0 && j-1<0) dp[i][j]={i-1,j};
else if (i-1<0 && j-1>=0) dp[i][j]={i,j-1};
s+=c[n-1][m-1];
Rec(dp[n-1][m-1].F,dp[n-1][m-1].S);
reverse(s.begin(),s.end());
cout << s;
}
