#define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
#define int long long
#define YES cout<<"YES\n"
#define NO cout<<"NO\n"
#define endl "\n"
#define debug cout<<'*'<<'\n'
const int N = 2e5+50, M = 2e6+50;
const int mod = 1e9 + 7, inf = 2e18;
using namespace std;
struct Edge
{
	int to, next, w;
}edge[M * 2];
int tot = 1, head[N];

int n_all, s, t;

void add(int u, int v, int w)
{
	edge[++tot].to = v;
	edge[tot].next = head[u];
	edge[tot].w = w;
	head[u] = tot;
}

int d[N],cur[N];
void bfs()//分层
{
	for (int i = 1; i <= n_all; i++)d[i] = -1,cur[i]=head[i];
	d[s] = 0;
	queue<int>q;
	q.push(s);
	while (!q.empty())
	{
		int u = q.front();
		q.pop();
		for (int i = head[u]; i; i = edge[i].next)
		{
			int v = edge[i].to;
			if (edge[i].w > 0 && d[v] == -1)
			{
				d[v] = d[u] + 1;
				q.push(v);
			}
		}
	}
}

int dfs(int u, int flow)//算流量
{
	if (u == t)return flow;
	int rmn = flow;
	for (int &i = cur[u]; i&&rmn; i = edge[i].next)
	{
		int v = edge[i].to;
		if (edge[i].w > 0 && d[v] == d[u] + 1)
		{
			int c = dfs(v, min(rmn, edge[i].w));
			rmn -= c;
			edge[i].w -= c;
			edge[i ^ 1].w += c;
		}
	}
	return flow - rmn;
}
int col[N],row[N];
void solve() {
	int n,m,a,b;
	cin>>n>>m>>a>>b;
	n_all = n+m+2;
	s=n+m+1,t=n+m+2;
	tot=1;
	for(int i=1;i<=n;i++) {
		add(s,i,0);
		col[i]=tot;
		add(i,s,0);
	}
	for(int j=1;j<=m;j++) {
		add(j+n,t,0);
		row[j]=tot;
		add(t,j+n,0);
	}
	int cnt=0;
	for(int i=1;i<=n;i++) {
		for(int j=1;j<=m;j++) {
			char c;
			cin>>c;
			if(c=='.') {
				add(i,j+n,1);
				add(j+n,i,0);
				cnt++;
			}
		}
	}
	int ans=b*cnt;
	for(int k=1;k<=min(n,m);k++) {
		for(int i=1;i<=n;i++)edge[col[i]].w+=1;
		for(int j=1;j<=m;j++)edge[row[j]].w+=1;
		do {
			bfs();
			cnt-=dfs(s,inf);
		}while(d[t]!=-1);
		ans=min(ans,a*k+b*cnt);
	}

	cout<<ans;
}
signed main()
{
	//freopen("C:\\Users\\win11\\Desktop\\test.txt", "r", stdin);
	//ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

	int T = 1;
	//cin >> T;
	while (T--)solve();
}