#include <bits/stdc++.h>

using namespace std;

bool isok(int a, int b, int c)
{
  if(max({a, b, c}) == b) return (true);
  if(min({a, b, c}) == b) return (true);
  return (false);
}

int main()
{
  char x, y, z;
  cin >> x >> y >> z;
  if(z == '?') swap(z, x);

  string ret;

  if(x == '?') {
    if(isok('1', y, z)) ret += "1";
    if(isok('4', y, z)) ret += "4";
  } else {
    if(isok(x, '1', z)) ret += "1";
    if(isok(x, '4', z)) ret += "4";
  }
  cout << ret << endl;
}