#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int main(){
    int h, w; cin >> h >> w;
    vector<string> s(h);
    for(auto &it: s) cin >> it;

    vector<vector<vector<int>>> cnt(h+w, vector<vector<int>>(26));
    cnt[0][s[0][0]-'a'].emplace_back(0);
    vector<vector<int>> pre(h, vector<int>(w, -1));
    for(int phase = 0; phase < h+w-1; phase++){
        for(int x = 0; x < 26; x++){
            if(cnt[phase][x].size() == 0) continue;
            for(auto &it: cnt[phase][x]){
                int i = it/w, j = it%w;
                // cerr << i << " " << j << ", ";
                if(i+1 < h && pre[i+1][j] == -1){
                    cnt[phase+1][s[i+1][j]-'a'].emplace_back((i+1)*w+j);
                    pre[i+1][j] = i*w+j;
                }
                if(j+1 < w && pre[i][j+1] == -1){
                    cnt[phase+1][s[i][j+1]-'a'].emplace_back(i*w+j+1);
                    pre[i][j+1] = i*w+j;
                }
            }
            // cerr << endl;
            break;
        }
    }

    string ans = "";
    int cur = (h-1)*w+w-1;
    while(cur != -1){
        ans += s[cur/w][cur%w];
        cur = pre[cur/w][cur%w];
    }
    reverse(ans.begin(), ans.end());
    cout << ans << endl;
    return 0;
}