#include<stdio.h>
int main(void){
	char a[100],b[100];
	char x,y;
	long a1,b1;
	scanf("%s%ld%c",a,&a1,&x);
	scanf("%s%ld%c",b,&b1,&y);
	if(a1 == b1){
		printf("-1\n");
	}else if(a1 > b1){
		printf("%s\n",a);
	}else if(b1 > a1){
		printf("%s\n",b);
	}
	return 0;
}