#include<stdio.h>

int main(void){
	int a,b,ad,bd,k=1000000000;
	scanf("%d%d",&a,&b);
	while(1){
		ad = (a/k)%10;
		bd = (b/k)%10;
		if(ad == 4 && bd == 7){printf("%d\n",a);return 0;}
		if(ad == 7 && bd == 4){printf("%d\n",b);return 0;}
		if(ad > bd){printf("%d\n",a);return 0;}
		if(ad < bd){printf("%d\n",b);return 0;}
		k/=10;
	}
	return 0;
}