#include<bits/stdc++.h>
#include<atcoder/all>
using namespace atcoder;
//using mint = modint1000000007;
using mint = modint998244353;
//g++ -I/opt/ac-library ./**.cpp
using namespace std;
using ll = long long;
using ull = unsigned long long;
//const long long MOD = 1000000007;
const long long MOD = 998244353;
const long double PI = 3.14159265358979;
const long long INF = 1LL<<60;
template <typename T> bool chmax(T &a, const T& b){if(a < b){a = b;return true;}return false;}
template <typename T> bool chmin(T &a, const T& b){if(a > b){a = b;return true;}return false;}
#define deb(var) do{cout << #var << " : "; view(var);}while(0)
template<typename T> void view(T e){cout << e << endl;}
void view(vector<string>& v){cout << endl;for(auto& s :v){view(s);}cout << endl;}
template<typename T> void view(vector<T>& v){for(auto& e :v){cout << e << " ";}cout << endl;}
template<typename T> void view(vector<vector<T>>& vv){cout << endl;for(auto& v:vv){view(v);}}
ll gcd(ll a, ll b){if (b == 0) return a;else return gcd(b, a % b);}
ll lcm(ll x,ll y){return ll(x/gcd(x,y))*y;}
template<typename T> using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define int long long

using ld = long double;

int32_t main() {
    int h, w; cin >> h >> w;
    vector<string> s(h);
    for (int i=0; i<h; i++) {
        cin >> s[i];
    }
    vector<vector<ld>> dp(h, vector<ld> (w, 0.0));
    for (int i=h-1; i>=0; i--) {
        for (int j=w-1; j>=0; j--) {
            ld c = ld(s[i][j] - 'a');
            if (i == h - 1 && j == w - 1) {
                dp[i][j] = c/26.0;
                continue;
            }
            if (i == h - 1) {
                dp[i][j] = (dp[i][j + 1] + c)/26.0;
                continue;
            }
            if (j == w - 1) {
                dp[i][j] = (dp[i + 1][j] + c)/26.0;
                continue;
            }
            if (dp[i + 1][j] < dp[i][j + 1]) {
                dp[i][j] = (dp[i + 1][j] + c)/26.0;
            }
            else {
                dp[i][j] = (dp[i][j + 1] + c)/26.0;
            }
        }
    }
    int i = 0, j = 0;
    string ans;
    while (!(i == h - 1 && j == w - 1)) {
        ans.push_back(s[i][j]);
        if (i == h - 1) {
            j++;
            continue;
        }
        if (j == w - 1) {
            i++;
            continue;
        }
        if (dp[i + 1][j] < dp[i][j + 1]) i++;
        else j++;
    }
    ans.push_back(s[i][j]);
    cout << ans << "\n";
}