#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

bool Comp(const string& lh, const string& rh)
{
  if (lh.size() != rh.size()){
    return lh.size() < rh.size();
  }
  return lexicographical_compare(lh.begin(), lh.end(), rh.begin(), rh.end());
}

void RemoveZero(string& s)
{
  while (!s.empty() && s[0] == '0'){
    s.erase(0, 1);
  }
}

main()
{
  int w, h;
  while (cin >> w >> h && w){
    string answer = "0";
    string table[70];

    for (int i = 0; i < h; ++i){
      for (int j = 0; j < w; ++j){
	char c;
	cin >> c;

	if (!isdigit(c)){
	  table[j] = "";
	  continue;
	}
	
	string up, left;
	up = table[j] + c;
	RemoveZero(up);

	if (j != 0){
	  left = table[j - 1] + c;
	  RemoveZero(left);
	}

	if (Comp(up, left)){
	  table[j] = left;
	} else {
	  table[j] = up;
	}
	if (Comp(answer, table[j])){
	  answer = table[j];
	}
      }
    }
    cout << answer << endl;
  }
  
}