#include <stdio.h>
#include <string.h>
#include <iostream>
#include <math.h>


using namespace std;

int main(){
    int a,b,n = 1000000000;
    bool flag = true;
    scanf("%d %d",&a,&b);
    for(;n > 0;n /= 10){
        int aa = a / n % 10,bb = b / n % 10;
        if(aa == bb)continue;
        if(aa < bb)flag = false;
        if(aa == 4 && bb == 7 or aa == 7 && bb == 4)flag = !(flag);
        break;
    }
    printf("%d\n",flag ? a : b);
    
    return 0;
}