#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> du;
typedef tuple<ll,ll,ll> tri;
#define INF 1e16
#define pi acos(-1)
#define mod 998244353
#define base 13331
const int MAXN=200005;
const int MAXC=30;
const int siz=270;
const int maxnode = 1e6+5;
const int up = 30;;
struct edge{
  int to, rev;
  ll cap;
  edge(int t=0, ll c=0, int r=0):to(t), cap(c), rev(r) {}
};
struct max_flow {
  vector<vector<edge> > G;
  vector<int> level, iter;
  int n,rem=0;
  max_flow(int n=0):n(n), G(n), level(n), iter(n) {}
  inline int add(int from, int to, ll cap) {
    G[from].emplace_back(to, cap, G[to].size());
    G[to].emplace_back(from, 0, G[from].size()-1);
    return G[from].size()-1;
  }
  void bfs(int s) {
    for(int i = 0; i < n; i++) level[i] = -1;
    queue<int> que;
    level[s] = 0;
    que.emplace(s);
    while(!que.empty()) {
      int now = que.front();
      que.pop();
      for(edge &e:G[now]) {
        if(e.cap > 0 and level[e.to] < 0) {
          level[e.to] = level[now] + 1;
          que.emplace(e.to);
        }
      }
    }
  }
  ll dfs(int v, int t, ll f) {
    if(v == t) return f;
    for(int &i = iter[v]; i < G[v].size(); i++) {
      edge &e = G[v][i];
      if(e.cap > 0 and level[v] < level[e.to]) {
        ll d = dfs(e.to, t, min(f, e.cap));
        if(d > 0) {
          e.cap -= d;
          G[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }
  ll Dinic(int s, int t) {
    ll flow = rem;
    while(true) {
      bfs(s);
      if(level[t] < 0) {
		  rem=flow;
		  return flow;
	  }
      for(int i = 0; i < n; i++) iter[i] = 0;
      ll f;
      while((f = dfs(s, t, INT64_MAX)) > 0) flow += f;
    }
  }
};
ll n,m,c,d,ans;
string s[505];
void solve(){
    cin>>n>>m>>c>>d;
	for(ll i=0;i<n;i++)
		cin>>s[i];
	ans=INF;
	int cnt = 0;
	max_flow f(1005);
	for(ll i=1;i<=n;i++)
			for(ll j=1;j<=m;j++){
				if(s[i-1][j-1]=='.'){
					f.add(i,n+j,1);
                    cnt++;
                }
			}
	ans=min(ans,c*0+d*(cnt-f.Dinic(0,n+m+1)));
	for(ll k=1;k<=max(n,m);k++){
		for(ll i=1;i<=n;i++)
			f.add(0,i,1);
		for(ll i=1;i<=m;i++)
			f.add(n+i,n+m+1,1);
		ans=min(ans,c*k+d*(cnt-f.Dinic(0,n+m+1)));
	}
	cout<<ans<<endl;
}
int main(){
    ios::sync_with_stdio(0);
    ll t=1;
    //cin>>t;
    while(t--)
        solve();
    return 0;
}