#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
using namespace std;

int main() {
  int A,B,N,M,a=0,b=0;
  cin>>A>>B>>N>>M;
  if(A==B){
    cout<<A<<"\n";
  }
  if(A<B){
    if(B-A>=M){
      for (size_t i = 0; i < (B-A)/M; i++) {
        a++;
      }
      cout<<A+a<<"\n";
    }else{
      cout<<A<<"\n";
    }
  }
  if(B<A){
    if(A-B>=N){
      for (size_t i = 0; i < (A-B)/N; i++) {
        b++;
      }
      cout<<B+b<<"\n";
    }else{
      cout<<B<<"\n";
    }
  }
}