#pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") #include <bits/stdc++.h> #include <atcoder/all> using namespace std; using namespace atcoder; typedef long long ll; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--) #define repk(i, k, n) for (int i = k; i < (int)(n); i++) #define all(v) v.begin(), v.end() #define mod1 1000000007 #define mod2 998244353 #define vi vector<int> #define vs vector<string> #define vc vector<char> #define vl vector<ll> #define vvi vector<vector<int>> #define vvc vector<vector<char>> #define vvl vector<vector<ll>> #define vvvi vector<vector<vector<int>>> #define vvvl vector<vector<vector<ll>>> #define pii pair<int,int> #define pil pair<int,ll> #define pli pair<ll, int> #define pll pair<ll, ll> #define vpii vector<pair<int,int>> #define vpll vector<pair<ll,ll>> #define vvpii vector<vector<pair<int,int>>> #define vvpll vector<vector<pair<ll,ll>>> template<typename T> void debug(T e){ cerr << e << endl; } template<typename T> void debug(vector<T> &v){ rep(i, v.size()){ cerr << v[i] << " "; } cerr << endl; } template<typename T> void debug(vector<vector<T>> &v){ rep(i, v.size()){ rep(j, v[i].size()){ cerr << v[i][j] << " "; } cerr << endl; } } template<typename T> void debug(vector<pair<T, T>> &v){ rep(i,v.size()){ cerr << v[i].first << " " << v[i].second << endl; } } template<typename T> void debug(set<T> &st){ for (auto itr = st.begin(); itr != st.end(); itr++){ cerr << *itr << " "; } cerr << endl; } template<typename T> void debug(multiset<T> &ms){ for (auto itr = ms.begin(); itr != ms.end(); itr++){ cerr << *itr << " "; } cerr << endl; } template<typename T> void debug(map<T, T> &mp){ for (auto itr = mp.begin(); itr != mp.end(); itr++){ cerr << itr->first << " " << itr->second << endl; } } void debug_out(){ cerr << endl; } template <typename Head, typename... Tail> void debug_out(Head H, Tail... T){ cerr << H << " "; debug_out(T...); } int main(){ int H, W; cin >> H >> W; vector<string> S(H); rep(i,H) cin >> S[i]; vector<vector<int>> vec(H, vector<int>(W)); rep(i,H){ rep(j,W){ vec[i][j] = (int)(S[i][j] - 'a'); } } string ans = ""; vector<vector<bool>> can(H, vector<bool>(W, false)); can[0][0] = true; ans += S[0][0]; for (int i = 0; i < H + W - 2; i++){ int min_vec = 27; for (int j = 0; j < H; j++){ if (i - j < 0 || i - j >= W){ continue; } if (can[j][i - j]){ if (j + 1 < H){ min_vec = min(min_vec, vec[j + 1][i - j]); } if (i - j + 1 < W){ min_vec = min(min_vec, vec[j][i - j + 1]); } } } for (int j = 0; j < H; j++){ if (i - j < 0 || i - j >= W){ continue; } if (can[j][i - j]){ if (j + 1 < H){ if (vec[j + 1][i - j] == min_vec){ can[j + 1][i - j] = true; } } if (i - j + 1 < W){ if (vec[j][i - j + 1] == min_vec){ can[j][i - j + 1] = true; } } } } //debug(min_vec); ans += (char)(min_vec + 'a'); } //debug(can); cout << ans << endl; }