#include <iostream>
#include <cmath>
#include <algorithm>

int main(int argc, char const *argv[]) {
  int a,b,n,m;
  std::cin >> a>>b>>n>>m;
  while (a-b>n || b-a>m) {
    if (a>b) {
      a-=n;
      b+=1;
    }else{
      b-=m;
      a+=1;
    }
  }
  std::cout << std::min(a,b) << '\n';
  return 0;
}