#include <cstdio>
#include <cstring>
using namespace std;

const int N = 555;
long long ans; char s[N];

int n,m,tot,sum,flow,a,b,l,r,S,T;
int st[N],id[2][N],dep[N],q[N];
struct edge{ int to,next,flow; } g[N * N];

int min(int x,int y) { return x < y ? x : y; }

void read(int &x)
{
	char c = getchar(); x = 0;
	while(c < '0' || c > '9') c = getchar();
	while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
}

void add(int u,int v,int w)
{ g[++tot] = (edge){ v,st[u],w }, st[u] = tot; }

void add_edge(int u,int v,int w) { add(u,v,w), add(v,u,0); }

int BFS()
{
	for(int i = 1;i <= T; ++ i) dep[i] = 0;
	
	dep[q[l = r = 1] = S] = 1;
	for(int x;x = q[l], l <= r; ++ l)
		for(int i = st[x],v;i;i = g[i].next)
			if(g[i].flow && !dep[v = g[i].to])
				dep[v] = dep[x] + 1, q[++r] = v;
	return dep[T];
}

int dinic(int x,int flow)
{
	if(x == T) return flow;
	
	int rest = 0;
	for(int i = st[x],v,tmp;i;i = g[i].next)
		if(g[i].flow && dep[v = g[i].to] == dep[x] + 1)
		{
			tmp = dinic(v,min(g[i].flow,flow)),
			flow -= tmp, rest += tmp, g[i].flow -= tmp, g[i ^ 1].flow += tmp;
			if(!flow) return rest;
		}
	
	if(!rest) dep[x] = 0;
	return rest;
}

int main()
{
	read(n), read(m), read(a), read(b),
	sum = flow = 0, S = n + m + 1, T = S + 1, tot = 1;
	
	for(int i = 1;i <= n; ++ i) id[0][i] = tot + 1, add_edge(S,i,0);
	for(int i = 1;i <= m; ++ i) id[1][i] = tot + 1, add_edge(i + n,T,0);
	for(int i = 1;i <= n; ++ i)
	{
		scanf(" %s",s + 1);
		for(int j = 1;j <= m; ++ j)
			if(s[j] == '.') ++sum, add_edge(i,j + n,1);
	}
	
	ans = 1ll * b * (sum - flow);
	for(int k = 1,flag;k <= n; ++ k)
	{
		flag = 1;
		for(int i = 1;i <= n; ++ i) ++g[id[0][i]].flow;
		for(int i = 1;i <= m; ++ i) ++g[id[1][i]].flow;
		
		while(BFS()) flow += dinic(S,n * m), flag = 0;
		if(flag == 1) break;
		ans = min(ans,1ll * k * a + 1ll * b * (sum - flow));
	}
	printf("%lld\n",ans);
	
	return 0;
}