#include<bits/stdc++.h>
using namespace std;
int n,m,k1,k2,ans=(1<<30),b[30][2];
bool vis[60][60];
void dfs(int x,int y,int now,int ma)
{
	if(vis[x-1][y]&&vis[x+1][y]&&!vis[x][y+1]&&!vis[x][y-1]) return;
	if(!vis[x-1][y]&&!vis[x+1][y]&&vis[x][y+1]&&vis[x][y-1]) return;
	if(ma>ans) return;
	if(now<=((n*m)>>1))
	{
		b[now][0]=x;
		b[now][1]=y;
	}
	else ma=max(ma,abs(b[now-n*m/2][0]-x)*k1+abs(b[now-n*m/2][1]-y)*k2);
	if(now==n*m)
	{
		if(ma<ans) ans=ma;
		return;
	}
	if(!vis[x-1][y])
	{
		vis[x-1][y]=1;
		dfs(x-1,y,now+1,ma);
		vis[x-1][y]=0;
	}
	if(!vis[x+1][y])
	{
		vis[x+1][y]=1;
		dfs(x+1,y,now+1,ma);
		vis[x+1][y]=0;
	}
	if(!vis[x][y-1])
	{
		vis[x][y-1]=1;
		dfs(x,y-1,now+1,ma);
		vis[x][y-1]=0;
	}
	if(!vis[x][y+1])
	{
		vis[x][y+1]=1;
		dfs(x,y+1,now+1,ma);
		vis[x][y+1]=0;
	}
	return;
}
int main()
{
	freopen("mmatrix.in","r",stdin);
	freopen("mmatrix.out","w",stdout);
	scanf("%d%d%d%d",&n,&m,&k1,&k2);
	for(int i=0;i<=n+1;i++)
	{
		vis[i][0]=1;
		vis[i][m+1]=1;
	}
	for(int i=0;i<=m+1;i++)
	{
		vis[0][i]=1;
		vis[n+1][i]=1;
	}
	vis[1][1]=1;
	dfs(1,1,1,0);
	printf("%d",ans);
    return 0;
}