#include<iostream>
using namespace std;
bool great(int x,int y){
    if(x == 4 && y == 7) return false;
    if(y == 4 && x == 7) return true;
    else return x < y;
}
int main(){
    int A,B,A_,B_;
    bool ans;
    int numA[10] = {};
    int numB[10] = {};
    cin >> A >> B;
    A_ = A;
    B_ = B;
    for(int i=9;i>=0;i--){
        numA[i] = A%10;
        A /= 10;
        numB[i] = B%10;
        B /= 10;
    }
    for(int i=0;i<10;i++){
        if(numA[i] == numB[i]) continue;
        else if(great(numA[i],numB[i])){
            ans = true;
        }
        else ans = false;
        break;
    }
    if(ans) cout << B_ << endl;
    else cout << A_ << endl;
    return 0;
}