#include<bits/stdc++.h>
using namespace std;
long long n,m,k,c,d,t1,t2,S(1e18),a[305],b[305]; char s[305];
int main(){scanf("%d%d%d%d",&n,&m,&c,&d);
	for(int i=1;i<=n;i++){scanf("%s",s+1);
		for(int j=1;j<=m;j++)
			if(s[j]=='.') a[i]++,b[j]++
			,k=max(k,max(a[i],b[i]));}
	//printf("%d %d %d\n",c,k,S);
	for(long long i=k;~i;i--){t1=t2=0;
		for(int j=1;j<=n;j++) t1+=max(0ll,a[j]-i);
		for(int j=1;j<=m;j++) t2+=max(0ll,b[j]-i);
		S=min(S,c*i+d*max(t1,t2));}
	printf("%lld\n",S); return 0;
}