#include<iostream>
#include<fstream>
using namespace std;
long long cx,co,maxx,maxo;
long long min(long long x,long long y)
{
  if (x<y) return x;
  else return y;
}
int main()
{
	ifstream fin("bs.in");
	ofstream fout("bs.out");
	while (fin.eof()==false)
	{
		fin>>co>>cx>>maxo>>maxx;
	if (min(maxo,co)==0) fout<<min(maxx,cx)<<endl;
	else
	if (min(maxx,cx)==0) fout<<min(maxo,co)<<endl;
	else
	if ((co)>(cx+1)*maxo) 
		fout<<((cx+1)*maxo+cx)<<endl;
	else
	if ((cx)>(co+1)*maxx)
		fout<<((co+1)*maxx+co)<<endl;
	else
	fout<<cx+co<<endl;
	}
	fin.close();
	fout.close();
	return 0;
}