#include <iostream>
using namespace std;
int main(){
    long long a,b,c,d;cin>>a>>b>>c>>d;
    long long mn = 0;
    long long mx = 1000000000000000001;
    while(mx-mn > 1){
        long long ce = (mx+mn)/2;
        if(ce <= a && ce <= b){
            mn = ce;
        }else if(ce <= a && ce <= (a-ce)/c+b){
            mn = ce;
        }else if(ce <= b && ce <= (b-ce)/d+a){
            mn = ce;
        }else{
            mx = ce;
        }
    }
    cout << mn << endl;
}