#include <fstream>
using namespace std;
ifstream cin("bs.in");
ofstream cout("bs.out");
int co,cx,mo,mx;
int main()
{
	while (!cin.eof())
	{
		co=-1;
		cin>>co>>cx>>mo>>mx;
		if (co!=-1)
		{
			if (mo==0&&mx==0) cout<<0<<endl;else
			{
				if (mo==0) cout<<mx<<endl;else
					if (mx==0) cout<<mo<<endl;else
					{
						if (co>(cx+1)*mo) cout<<(cx+1)*mo+cx<<endl;else
							if (cx>(co+1)*mx) cout<<(co+1)*mx+co<<endl;else
								cout<<co+cx<<endl;
					}
			}
		}
	}
	return 0;
}