#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000001
	

int main(){
	
	long long A,B,N,M;
	cin>>A>>B>>N>>M;
	
	if(A<B){
		swap(A,B);
		swap(N,M);
	}
	
	long long ok = 0LL,ng = Inf;
	
	while(ng-ok>1LL){
		long long mid = (ok+ng)/2;
		if(A<mid){
			ng = mid;
			continue;
		}
		if(B + (A-mid)/N < mid)ng = mid;
		else ok = mid;
	}
	
	cout<<ok<<endl;
	
    return 0;
}