#include <bits/stdc++.h>
using namespace std;
int main(void){
    long long A,B,N,M,sa,mc;cin >> A >> B >> N >> M;
    if(B>A){
        sa=B-A;
        mc=A;
        for(;;){
            if(sa>M){
            sa=sa-M;
            mc++;
        }else{
            break;
        }
        }
        cout << mc << endl;
        return 0;
    }else if(A>B){
        sa=A-B;
        mc=B;
        for(;;){
            if(sa>N){
            sa=sa-N;
            mc++;
        }else{
            break;
        }
        }
        cout << mc << endl;
        return 0;
    }
    
}