#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

struct Node {
  int y;
  int x;
  char ch;

  Node(int y = -1, int x = -1, char ch = -1) {
    this->y = y;
    this->x = x;
    this->ch = ch;
  }

  bool operator>(const Node &n) const {
    return ch > n.ch;
  }
};

int main() {
  int H, W;
  cin >> H >> W;

  vector<string> S(H);
  for (int y = 0; y < H; ++y) {
    cin >> S[y];
  }

  priority_queue <Node, vector<Node>, greater<Node>> pque;
  pque.push(Node(0, 0, S[0][0]));

  int history[H][W];
  memset(history, -1, sizeof(history));

  while (not pque.empty()) {
    Node node = pque.top();
    pque.pop();

    if (node.y + 1 < H && history[node.y + 1][node.x] == -1) {
      history[node.y + 1][node.x] = 2;
      pque.push(Node(node.y + 1, node.x, S[node.y + 1][node.x]));
    }

    if (node.x + 1 < W && history[node.y][node.x + 1] == -1) {
      history[node.y][node.x + 1] = 1;
      pque.push(Node(node.y, node.x + 1, S[node.y][node.x + 1]));
    }
  }

  string ans = "";
  int cy = H - 1;
  int cx = W - 1;
  while (cy != 0 || cx != 0) {
    int dir = history[cy][cx];
    ans += S[cy][cx];

    if (dir == 1) {
      cx -= 1;
    } else {
      cy -= 1;
    }
  }
  ans += S[0][0];

  reverse(ans.begin(), ans.end());
  cout << ans << endl;

  return 0;
}