#include<stdio.h>

void run(void){
  int a,b;
  scanf("%d%d",&a,&b);

  int d=1000000000;
  while(a/d==0 && b/d==0){
    d/=10;
  }
  if(a/d==0 && b/d>0){
    printf("%d\n",b);
    return;
  }
  if(a/d>0 && b/d==0){
    printf("%d\n",a);
    return;
  }

  while(d>0){
    int x,y;
    x=(a/d)%10;
    y=(b/d)%10;
    if(x!=y){
      if(x==4 && y==7){
        printf("%d\n",a);
      } else if(x==7 && y==4){
        printf("%d\n",b);
      } else {
        printf("%d\n",a<b?a:b);
      }
      return;
    }
    d/=10;
  }
}

int main(void){
  run();
  return 0;
}