#include<fstream>
#include<string>
#include<algorithm>

using namespace std;
ifstream fi("bs.in");
ofstream fo("bs.out");

int maxX,maxO,countX,countO,ok=0;

int mini(int a,int b)
{
	if(a>=b)
		return b;
	else
		return a;
}
int main()
{
	while(!fi.eof())
	{
		fi>>countO>>countX>>maxO>>maxX;
		if(countO!=0&&countX!=0&&maxO!=0&maxX!=0)
		{
			if(countO<=countX)
			{
				if((double)countX/(double)maxX<countO+1)
					fo<<countO+countX<<endl;
				else
					fo<<countO+maxX*(countO+1)<<endl;
			}
			else
			{
				if((double)countO/(double)maxO<countO+1)
					fo<<countO+countX<<endl;
				else
					fo<<countX+maxO*(countX+1)<<endl;
			}
		}
		else
		{
			if(maxO!=0&&maxX!=0)
				{fo<<mini(mini(maxO,countO),mini(maxX,countX))<<endl;ok=1;}
			if(maxO!=0&&!ok)
				{fo<<mini(maxO,countO)<<endl;ok=1;}
			if(maxX!=0&&!ok)
				{fo<<mini(maxX,countX)<<endl;ok=1;}
			if(!ok)
				fo<<0<<endl;
		}
	}
	fi.close();
	fo.close();
	return 0;
}