#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
constexpr int N = 1000, M = 2e5, inf = 1e9;
int n, m, c, d;
namespace FLOW {
	int n, s, t;
	int cnt, head[N], cur[N];
	struct Edge {
		int to, nxt, f;
	}e[M];
	int dep[N];
	void add(int u, int v, int f) {
		e[++ cnt] = {v, head[u], f}, head[u] = cnt;
		e[++ cnt] = {u, head[v], 0}, head[v] = cnt;
	}
	bool bfs() {
		for(int i = 1; i <= n; i ++) dep[i] = inf, cur[i] = head[i];
		queue<int> q;
		q.emplace(s); dep[s] = 0;
		while(!q.empty()) {
			int u = q.front(); q.pop();
			if(u == t) return true;
			for(int i = head[u]; i; i = e[i].nxt) if(e[i].f) {
				int v = e[i].to;
				if(dep[v] > dep[u] + 1) {
					dep[v] = dep[u] + 1;
					q.emplace(v);
				}
			}
		}
		return false;
	}
	int dfs(int u, int flow) {
		if(u == t) return flow;
		int res = flow;
		for(int &i = cur[u]; i; i = e[i].nxt) if(e[i].f) {
			int v = e[i].to;
			if(dep[v] == dep[u] + 1) {
				int k = dfs(v, min(res, e[i].f));
				e[i].f -= k, e[i ^ 1].f += k, res -= k;
				if(!res) return flow;
			}
		}
		return flow - res;
	}
	int maxflow() {
		int ans = 0;
		while(bfs()) ans += dfs(s, inf);
		return ans;
	}
}
int main() {
//	freopen("in.txt", "r", stdin);
	ios::sync_with_stdio(false), cin.tie(0);
	cin >> n >> m >> c >> d;
	FLOW::n = n + m + 2;
	FLOW::s = n + m + 1;
	FLOW::t = n + m + 2;
	FLOW::cnt = 1;
	for(int i = 1; i <= n; i ++) {
		FLOW::add(FLOW::s, i, 0);
	}
	for(int i = 1; i <= m; i ++) {
		FLOW::add(i + n, FLOW::t, 0);
	}
	int cnt = 0;
	for(int i = 1; i <= n; i ++){
		string str;
		cin >> str;
		str = "?" + str;
		for(int j = 1; j <= m; j ++) if(str[j] != '*') {
			FLOW::add(i, n + j, 1);
			cnt ++;
		}
	}
	int cur = 0;
	// cout << cnt << '\n';
	i64 ans = 1ll * cnt * d;
	for(int i = 1; i <= max(n, m); i ++) {
		int id = 2;
		for(int j = 1; j <= n; j ++, id += 2) {
			FLOW::e[id].f ++;
		}
		for(int j = 1; j <= m; j ++, id += 2) {
			FLOW::e[id].f ++;
		}
		cur += FLOW::maxflow();
		ans = min(ans, 1ll * (cnt - cur) * d + 1ll * i * c);
		// cout << i << ' ' << cur << '\n';
		if(cur == cnt) break;
	}
	cout << ans << '\n';
	return 0;
}