#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<cmath>
#include<algorithm>
#include<queue>
using namespace std;
#define FILE "read"
#define MAXN 2510
#define INF (int)1e9
const int dx[5]={1,0,-1,0};
const int dy[5]={0,1,0,-1};
struct node{int y,next,v;}e[MAXN*10];
int n,m,A,B,S,T,len(1),cnt,id[55][55],Link[MAXN],level[MAXN];
char map[55][55];
queue<int>q;
inline int read(){
	int x=0,f=1;  char ch=getchar();
	while(!isdigit(ch))  {if(ch=='-')  f=-1;  ch=getchar();}
	while(isdigit(ch))  {x=x*10+ch-'0';  ch=getchar();}
	return x*f;
}
void insert(int x,int y,int v){
	e[++len].next=Link[x];Link[x]=len;e[len].y=y;e[len].v=v;
	e[++len].next=Link[y];Link[y]=len;e[len].y=x;e[len].v=0;
}
bool bfs(){
	memset(level,-1,sizeof(level));
	q.push(S);  level[S]=0;
	while(!q.empty()){
		int x=q.front();  q.pop();
		for(int i=Link[x];i;i=e[i].next)if(level[e[i].y]<0&&e[i].v)
			q.push(e[i].y),level[e[i].y]=level[x]+1;
	}
	return level[T]>=0;
}
int MAXFLOW(int x,int flow){
	if(x==T)  return flow;
	int d=0,maxflow=0;
	for(int i=Link[x];i&&maxflow<flow;i=e[i].next)
		if(level[e[i].y]==level[x]+1&&e[i].v)
			if(d=MAXFLOW(e[i].y,min(e[i].v,flow-maxflow)))
				e[i].v-=d,e[i^1].v+=d,maxflow+=d;
	if(!maxflow)  level[x]=-1;
	return maxflow;
}
int main(){
	freopen(FILE".in","r",stdin);
	freopen(FILE".out","w",stdout);
	n=read();  m=read();  A=read();  B=read();  S=0;  T=n*m+1;
	for(int i=1;i<=n;++i)scanf("%s",map[i]+1);
	for(int i=1;i<=n;++i)for(int j=1;j<=m;++j)id[i][j]=++cnt;
	for(int i=1;i<=n;++i)for(int j=1;j<=m;++j){
		if(map[i][j]=='.')  insert(S,id[i][j],B);
		else insert(id[i][j],T,B);
		for(int k=0;k<4;++k){
			int x=i+dx[k],y=j+dy[k];
			if(x<=0||y<=0||x>n||y>m)  continue;
			insert(id[i][j],id[x][y],A);
		}
	}
	int d=0,ans=0;
	while(bfs()) while(d=MAXFLOW(S,INF)) ans+=d;
	printf("%d\n",ans);
	return 0;
}