// Problem: B. Cells Coloring
// Contest: Codeforces - The 2022 ICPC Asia Xian Regional Contest
// URL: https://codeforces.com/gym/104077/problem/B
// Memory Limit: 512 MB
// Time Limit: 1000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>

using LL = long long;

constexpr int N = 600, M = 150000, INF = 1E8;

int n, m, S, T;
int h[N], e[M], f[M], ne[M], idx;
int q[N], d[N], cur[N];

void addEdge(int a, int b, int c) {
	e[idx] = b, f[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;
}

void add(int a, int b, int c) {
    addEdge(a, b, c);
    addEdge(b, a, 0);
}

int find(int u, int limit) {
    if (u == T) {
    	return limit;
    }
    int flow = 0;
    for (int i = cur[u]; ~i and flow < limit; i = ne[i]) {
        cur[u] = i;
        int j = e[i];
        if (d[j] == d[u] + 1 and f[i]) {
            int t = find(j, std::min(f[i], limit - flow));
            if (t == 0) {
            	d[j] = -1;
            }
            f[i] -= t, f[i ^ 1] += t, flow += t;
        }
    }
    return flow;
}

bool bfs() {
    memset(d, -1, sizeof d);
    int hh = 0, tt = -1;
    q[ ++ tt] = S, d[S] = 0, cur[S] = h[S];
    while (hh <= tt) {
        auto t = q[hh ++ ];
        for (int i = h[t]; ~i; i = ne[i]) {
            int j = e[i];
            if (d[j] == -1 && f[i]) {
                d[j] = d[t] + 1;
                cur[j] = h[j];
                if (j == T) {
                	return true;
                }
                q[ ++ tt] = j;
            }
        }
    }
    return false;
}

int dinic() {
    int res = 0, flow;
    while (bfs()) {
    	while (flow = find(S, INF)) {
    		res += flow;
    	}
    }
    return res;
}

constexpr LL inf = 1E18;

int g[N][N];

void solve() {
	int n, m, c, d;
	std::cin >> n >> m >> c >> d;
	
	for (int i = 1; i <= n; i += 1) {
		for (int j = 1; j <= m; j += 1) {
			char c;
			std::cin >> c;
			g[i][j] = c == '.' ? 0: 1;
		}
	}
	S = 0, T = n + m + 1;
	
	int up = 0, tot = 0;
	for (int i = 1; i <= n; i += 1) {
		int cnt = 0;
		for (int j = 1; j <= m; j += 1) {
			cnt += g[i][j] == 0;
		}
		tot += cnt;
		up = std::max(up, cnt);
	}
	for (int j = 1; j <= m; j += 1) {
		int cnt = 0;
		for (int i = 1; i <= n; i += 1) {
			cnt += g[i][j];
		}
		up = std::max(up, cnt);
	}
	
	LL ans = inf;
	for (int k = 0; k <= up; k += 1) {
		memset(h, -1, sizeof h), idx = 0;
		memset(f, 0, sizeof f);
		for (int i = 1; i <= n; i += 1) {
			add(S, i, k);
		}
		for (int j = 1; j <= m; j += 1) {
			add(n + j, T, k);
		}
		for (int i = 1; i <= n; i += 1) {
			for (int j = 1; j <= m; j += 1) {
				if (!g[i][j]) {
					add(i, n + j, 1);
				}
			}
		}
		int cnt = dinic();
		LL cost = 1LL * c * k + 1LL * d * (tot - cnt);
		ans = std::min(ans, cost);
	}
	
	std::cout << ans << "\n";
}

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	
    int T = 1;
    // std::cin >> T;
    while (T -- ) {
    	solve();
    }
    
    return 0;
}