#include <stdio.h>
#include<string.h>
int main(void)
{
	char sa[100];
	char sb[100];
char pa[100000] ;
char pb[100000];
	char xa;
	char xb;
	scanf("%s%s%c",sa,pa,&xa);
	(void)getchar();
	scanf("%s%s%d",sb,pb);
	(void)getchar();
	scanf("%c",&xb);
	if(strlen(pa)>strlen(pb)){
		printf("%s\n",sa);
	}else if(strlen(pa)<strlen(pb)){
		printf("%s\n",sb);
		
	}else if(pa==pb){
		printf("-1\n");
	}
	
	return 0;
}