#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <sstream>
#include <complex>
#include <ctime>
#include <cassert>
#include <functional>

using namespace std;

typedef long long ll;
typedef vector<int> VI;
typedef pair<string,string> PSS;

#define REP(i,s,t) for(int i=(s);i<(t);i++)
#define FILL(x,v) memset(x,v,sizeof(x))

PSS read() {
  string s, a, b;
  cin >> s;
  REP(i,0,s.size()) {
    if (s[i] == '.') {
      a = s.substr(0, i);
      b = s.substr(i + 1);
      break;
    }
  }
  return PSS(a, b);
}
void print(PSS &v) {
  cout << v.first << "." << v.second << endl;
}
PSS normalize(string a, string b) {
  while (a.size() < b.size()) a += "0";
  while (b.size() < a.size()) b += "0";
  return PSS(a, b);
}

int main() {
  PSS x = read();
  PSS y = read();
  if (x.first != y.first) print(stoi(x.first) > stoi(y.first) ? x : y);
  else {
    PSS norm = normalize(x.second, y.second);
    if (((norm.first > norm.second) ^ (stoi(x.second) > stoi(y.second))) || stoi(x.second) == stoi(y.second)) cout << -1 << endl;
    else {
      print(norm.first > norm.second ? x : y);
    }
  }
  return 0;
}