#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <algorithm>
#include <sstream>
#include <map>
#include <set>
using namespace std;


#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;
typedef unsigned long long ull;
typedef long double lb;
/* ここからが本編 */

int main(void)
{
   ull i,j,k;
   char Sa[101];
   char Sb[101];
   char Pa[10005];
   char Pb[10005];
   char x;
   char winner = 0;
   cin >> Sa >> Pa >> x;
   cin >> Sb >> Pb >> x;
   if(strlen(Pa) > strlen(Pb) ) winner = 'a';
   if(strlen(Pa) < strlen(Pb) ) winner = 'b';
   else {
      for(j=0;j<strlen(Pa);j++) {
         if(Pa[j] > Pb[j]) {
            winner = 'a';break;
         }
         if(Pa[j] < Pb[j]) {
            winner = 'b'; break;
         }
      }
   }
   if(winner == 'a') cout << Sa << endl;
   if(winner == 'b') cout << Sb << endl;
   if(winner ==  0 ) cout << "-1" << endl;
   return 0;
}