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