#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
using T = tuple<int,int,int>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int h,w;
    cin >> h >> w;
    vector<int> ans(h+w-1,1001001001);
    vector<string> s(h);
    rep(i,h) cin >> s[i];
    priority_queue<asc(T)> pq;
    pq.push({0,s[0][0],0});
    vector<vector<bool>> seen(h,vector<bool>(w,false));
    seen[0][0] = true;
    while(pq.size()){
        int p,x,q;
        tie(p,x,q) = pq.top();
        pq.pop();
        if(ans[p]<x) continue;
        ans[p] = x;
        p -= q;
        if(p!=h-1 && !seen[p+1][q]) {pq.push({p+q+1,s[p+1][q],q}); seen[p+1][q] = true;}
        if(q!=w-1 && !seen[p][q+1]) {pq.push({p+q+1,s[p][q+1],q+1}); seen[p][q+1] = true;}
    }
    rep(i,h+w-1) cout << (char)ans[i];
    cout << '\n';
    return 0;
}