//这回只花了114514min就打完了。
//真好。记得多手造几组。
#include <bits/stdc++.h>
#define int long long
#define pai 3.141592653589793238462643383279502884197169399375105820
#define MOD 1000000007
#define eps 0.00000001
inline int min(int a,int b) {return a<b?a:b;}
inline int max(int a,int b) {return a>b?a:b;}
#define ULL unsigned long long
#define LL long long
#define INF 0x3f3f3f3f
#define INF_LL 0x3f3f3f3f3f3f3f3f
static char buf[1000000],*paa=buf,*pd=buf;
static char buf2[1000000],*pp=buf2;
#define getchar() paa==pd&&(pd=(paa=buf)+fread(buf,1,1000000,stdin),paa==pd)?EOF:*paa++
inline void pc(char ch){
	if(pp-buf2==1000000) fwrite(buf2,1,1000000,stdout),pp=buf2;
	*pp++=ch;
}
inline void pcc(){
	fwrite(buf2,1,pp-buf2,stdout);
	pp=buf2;
}
inline int read(void) {
	int w=1;
	register int x(0);register char c(getchar());
	while(c<'0'||c>'9') {if(c=='-') w=-1;c=getchar();}
	while(c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return w*x;
}
void write(int x) {
	if(x<0) pc('-'),x=-x;
	static int sta[20];
	int top=0;
	do {
		sta[top++]=x%10,x/=10;
	} while(x);
	while(top) pc(sta[--top]+48);
}
void we(int x) {
	write(x);
	pc('\n');
}
inline bool cmp_xi(int a,int b) {return a<b;}
inline bool cmp_da(int a,int b) {return a>b;}
int N,M,C,D,aq,v[2];
char s[259][259];
signed main(void) {
    //freopen("m.in","r",stdin);
    //freopen("m.out","w",stdout);
	scanf("%lld %lld %lld %lld",&N,&M,&C,&D);
	for(int i=1;i<=N;i++) {
    	scanf("%s",s[i]+1);
    	for(int j=1;j<=M;j++) {
    		if(s[i][j]=='.') aq++,v[(i^j)&1]++;
		}
	}
	int ans=std::min(2*C,aq*D);
	printf("%lld",std::min(ans,C+std::min(v[0],v[1])*D));
	return 0;
}