#include <iostream>
#include <cstdio>
#include <cstdlib>
//#define Max(a,b) a>b?a:b
#define Min(a,b) a<b?a:b
using namespace std;

int main()
{
	freopen("bs.in","r",stdin);
	freopen("bs.out","w",stdout);
	int tco,tcx,tmo,tmx;
	long long tmp;
	long long co,cx,mo,mx;
	while(scanf("%d %d %d %d\n",&tco,&tcx,&tmo,&tmx)==4)
	{
		co=tco;
		cx=tcx;
		mo=tmo;
		mx=tmx;
		if(co==0||mo==0)
		{
			tmp=Min(cx,mx);
			cout<<tmp<<endl;
			continue;
		}
		if(cx==0||mx==0)
		{
			tmp=Min(co,mo);
			cout<<tmp<<endl;
			continue;
		}
		
		if(co==cx)
		{
			cout<<co+cx<<endl;
			continue;
		}
		if(co<cx)
		{
			tmp=mx*(co+1);
			tmp=Min(tmp,cx);
			cout<<co+tmp<<endl;
			continue;
		}
		if(co>cx)
		{
			tmp=mo*(cx+1);
			tmp=Min(tmp,co);
			cout<<tmp+cx<<endl;
			continue;
		}
	}
	return 0;
}