#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

int main() {
  int H, W; cin >> H >> W;
  vector<string> S(H);
  for (int i = 0; i < H; i++) cin >> S[i];
  string ans = string(H * W - 1, 'z');
  queue<pair<int, string>> que;
  string s = string(1, S[0][0]);
  que.push({0, s});
  int dx[2] = {1, 0};
  int dy[2] = {0, 1};
  while (!que.empty()) {
    auto &[id, t] = que.front(); que.pop();
    int x = id / W;
    int y = id % W;
    if (x == H - 1 && y == W - 1) {
      ans = min(ans, t);
      continue;
    }
    for (int i = 0; i < 2; i++) {
      int nx = x + dx[i];
      int ny = y + dy[i];
      if (nx >= H || ny >= W) continue;
      que.push({nx * W + ny, t + S[nx][ny]});
    }
  }
  cout << ans << endl;
  return 0;
}