#include<iostream>
#include<algorithm>
#include<cstring>
#include<climits>
#define int long long
using namespace std;
const int N = 509, M = N * N,INF = INT_MAX;
char s[N][N];
int sc[N], cl[N],head[N],dis[N],gap[N],cur[N],q[N];
int total = 1,n,m,S,T,nod;
struct Edge {
	int next, to, flow;
}edge[M << 1];

void addedge(int u, int v, int val) {
	total++;
	edge[total].to = v;
	edge[total].flow = val;
	edge[total].next = head[u];
	head[u] = total;
}

void AddEdge(int u, int v, int w) {
	addedge(u, v, w);
	addedge(v, u, 0);
}

void bfs() {
	int Head = 0, Tail = 0;
	Tail++;
	q[Tail] = T;
	gap[dis[T]]++;
	dis[T] = 1;
	while (Head < Tail) {
		Head++;
		int x = q[Head];
		for (int i = head[x]; i; i = edge[i].next) {
			int y = edge[i].to;
			if ((!dis[y]) && edge[i ^ 1].flow) {
				dis[y] = dis[x] + 1;
				gap[dis[y]]++;
				Tail++;
				q[Tail] = y;
			}
		}
	}
}

int dfs(int x, int a) {
	if (x == T || (!a)) {
		return a;
	}
	int flow = 0, f;
	for (int& i = cur[x]; i; i = edge[i].next) {
		if (dis[x] == dis[edge[i].to] + 1) {
			f = dfs(edge[i].to, min(a, edge[i].flow));
			edge[i].flow -= f;
			edge[i ^ 1].flow += f;
			a -= f;
			flow += f;
			if (!a) {
				return flow;
			}
		}
	}
	gap[dis[x]]--;
	if (!gap[dis[x]]) {
		dis[S] = nod + 1;
	}
	dis[x]++;
	gap[dis[x]]++;
	return flow;
}

int ISAP() {
	static int ans = 0;
	bfs();
	while (dis[S] <= nod) {
		memcpy(cur + 1, head + 1, sizeof(*head) * nod);
		ans += dfs(S, INF);
	}
	return ans;
}

void solve() {
	int c = 0, d = 0, K = 0, sum = 0;
	cin >> n >> m >> c >> d;
	for (int i = 1; i <= n; i++) {
		cin >> (s[i] + 1);
		for (int j = 1; j <= m; j++) {
			if (s[i][j] == '.') {
				s[i][j] = 1;
			}
			else {
				s[i][j] = 0;
			}
			sc[i] += s[i][j];
			cl[j] += s[i][j];
			K = max(K, cl[j]);
		}
		K = max(K, sc[i]);
		sum += sc[i];
	}
	S = n + m + 1;
	T = nod = S + 1;
	for (int i = 1; i <= n; i++) {
		AddEdge(S, i, 0);
	}
	for (int i = 1; i <= m; i++) {
		AddEdge(i + n, T, 0);
	}
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= m; j++) {
			if (s[i][j]) {
				AddEdge(i, j + n, 1);
			}
		}
	}
	int ans = LLONG_MAX;
	for (int k = 0; k <= K; k++) {
		if (k) {
			memset(gap + 1, 0, sizeof(*gap) * nod);
			memset(dis + 1, 0, sizeof(*dis) * nod);
			for (int i = 1; i <= n; i++) {
				edge[i * 2].flow++;
			}
			for (int i = 1; i <= m; i++) {
				edge[(i + n) * 2].flow++;
			}
		}
		ans = min(ans, c * k + d * (sum - ISAP()));
	}
	cout << ans << endl;
}

signed main() {
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	solve();
	return 0;
}