#include <bits/stdc++.h>
using namespace std;

using pii = pair<int, int>;

const int MAXN = 65050;
struct edg{ int pos, cap, rev; };
struct Dinic{
	vector <edg> gph[MAXN];
	int dis[MAXN], pnt[MAXN], flow;
	void clear(){ for (int i = 0; i < MAXN; i++) gph[i].clear(); }
	pii add_edge(int s, int e, int x){
		gph[s].push_back({e, x, (int) gph[e].size()});
		gph[e].push_back({s, 0, (int) gph[s].size() - 1});
		return make_pair(s, gph[s].size() - 1);
	}
	bool bfs(int src, int sink){
		memset(dis, 0, sizeof dis);
		memset(pnt, 0, sizeof pnt);
		queue <int> que; 
		que.push(src), dis[src] = 1;
		while (que.size()){
			int x = que.front(); que.pop();
			for (auto &e : gph[x]){
				if (e.cap > 0 && !dis[e.pos]){
					dis[e.pos] = dis[x] + 1;
					que.push(e.pos);
				}
			}
		}
		return dis[sink] > 0;
	}
	int dfs(int x, int sink, int f){
		if (x == sink) return f;
		for (; pnt[x] < gph[x].size(); pnt[x]++){
			edg e = gph[x][pnt[x]];
			if (e.cap > 0 && dis[e.pos] == dis[x] + 1){
				int w = dfs(e.pos, sink, min(f, e.cap));
				if (w){
					gph[x][pnt[x]].cap -= w;
					gph[e.pos][e.rev].cap += w;
					return w;
				}
			}
		}
		return 0;
	}
	int max_flow(int src, int sink){
		while (bfs(src, sink)){
			int r;
			while ((r = dfs(src, sink, 2e9))) flow += r;
		}
		return flow;
	}
} G;

vector <pii> evec;

string mp[550];

int n, m, c, d, S, T, tot;

int main(){
	ios :: sync_with_stdio(false), cin.tie(0);
	cin >> n >> m >> c >> d;
	for (int i = 1; i <= n; i++)
		cin >> mp[i];
	S = 1, T = 2;
	for (int i = 1; i <= n; i++)
		evec.push_back(G.add_edge(S, 2 + i, 1));
	for (int i = 1; i <= m; i++)
		evec.push_back(G.add_edge(2 + n + i, T, 1));
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++){
			int id = (i - 1) * m + j;
			if (mp[i][j - 1] == '*') continue;
			tot++;
			G.add_edge(2 + i, 2 + n + m + id, 1);
			G.add_edge(2 + n + m + id, 2 + n + j, 1);
		}
	long long ret = 1ll * tot * d;
	for (int k = 1; k <= max(n, m); k++){
		int z = tot - G.max_flow(S, T);
		ret = min(ret, 1ll * c * k + 1ll * d * z);
		for (auto e : evec) G.gph[e.first][e.second].cap += 1;
	}
	cout << ret << endl;
	return 0;	
}