#include <bits/stdc++.h>
using namespace std;
#include <random>
typedef long long ll;
#define rep(i,a,b) for (int i=a; i<(b); ++i)
#define sz(x) (int)(x.size())
typedef vector<int> vi;
typedef pair<int,int> pii;

struct Dinic {
	struct Edge {
		int to, rev;
		ll c, oc;
		ll flow() { return max(oc - c, 0LL); }
	};

	vi lvl, ptr, q;
	vector<vector<Edge>> adj;
	Dinic(int n) : lvl(n), ptr(n), q(n), adj(n) {}

	void addEdge(int a, int b, ll c, ll rcap = 0) {
		adj[a].push_back({b, sz(adj[b]), c, c});
		adj[b].push_back({a, sz(adj[a]) - 1, rcap, rcap});
	}

	ll dfs(int v, int t, ll f) {
		if (v == t || !f) return f;
		for (int& i = ptr[v]; i < sz(adj[v]); i++) {
			Edge& e = adj[v][i];
			if (lvl[e.to] == lvl[v] + 1)
				if (ll p = dfs(e.to, t, min(f, e.c))) {
					e.c -= p, adj[e.to][e.rev].c += p;
					return p;
				}
		}
		return 0;
	}

	ll calc(int s, int t) {
		ll flow = 0; q[0] = s;
		do {
			lvl = ptr = vi(sz(q));
			int qi = 0, qe = lvl[s] = 1;
			while (qi < qe && !lvl[t]) {
				int v = q[qi++];
				for (Edge e : adj[v])
					if (!lvl[e.to] && e.c)
						q[qe++] = e.to, lvl[e.to] = lvl[v] + 1;
			}
			while (ll p = dfs(s, t, LLONG_MAX)) flow += p;
		} while (lvl[t]);
		return flow;
	}
	bool leftOfMinCut(int a) { return lvl[a] != 0; }
};

int n,m;
ll c,d,cnt,ans[300];
string s[255];

ll solve(int k) {
	if (ans[k]!=-1) return ans[k];

	Dinic dnc=Dinic(n+m+2);
	for (int i=0; i<n; ++i) for (int j=0; j<m; ++j) if (s[i][j]=='.') dnc.addEdge(i,j+n,1);
	for (int i=0; i<n; ++i) dnc.addEdge(n+m,i,k);
	for (int i=n; i<n+m; ++i) dnc.addEdge(i,n+m+1,k);
	ll res=dnc.calc(n+m,n+m+1);
	ans[k]=c*k+d*(cnt-res);
	return ans[k];
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
	memset(ans,-1,sizeof(ans));
    cin>>n>>m>>c>>d;
    for (int i=0; i<n; ++i) cin>>s[i];
    for (int i=0; i<n; ++i) for (int j=0; j<m; ++j) if (s[i][j]=='.') ++cnt;
	ans[0]=cnt*d;

	int l=1, r=250;
	while (l<r) {
		int mid=(l+r+1)/2;
		if (solve(mid-1)>=solve(mid)) l=mid;
		else r=mid-1;
	}
    
    cout<<min(ans[0],ans[l])<<"\n";
}