#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
const i64 P = 998244353;
template <typename T> struct Flow_ {
    const int n;
    const T inf = numeric_limits<T>::max();
    struct Edge {
        int to;
        T w;
        Edge(int to, T w) : to(to), w(w) {}
    };
    vector<Edge> ver;
    vector<vector<int>> h;
    vector<int> cur, d;
    
    Flow_(int n) : n(n + 1), h(n + 1) {}
    void add(int u, int v, T c) {
        h[u].push_back(ver.size());
        ver.emplace_back(v, c);
        h[v].push_back(ver.size());
        ver.emplace_back(u, 0);
    }
    bool bfs(int s, int t) {
        d.assign(n, -1);
        d[s] = 0;
        queue<int> q;
        q.push(s);
        while (!q.empty()) {
            auto x = q.front();
            q.pop();
            for (auto it : h[x]) {
                auto [y, w] = ver[it];
                if (w && d[y] == -1) {
                    d[y] = d[x] + 1;
                    if (y == t) return true;
                    q.push(y);
                }
            }
        }
        return false;
    }
    T dfs(int u, int t, T f) {
        if (u == t) return f;
        auto r = f;
        for (int &i = cur[u]; i < h[u].size(); i++) {
            auto j = h[u][i];
            auto &[v, c] = ver[j];
            auto &[u, rc] = ver[j ^ 1];
            if (c && d[v] == d[u] + 1) {
                auto a = dfs(v, t, std::min(r, c));
                c -= a;
                rc += a;
                r -= a;
                if (!r) return f;
            }
        }
        return f - r;
    }
    T work(int s, int t) {
        T ans = 0;
        while (bfs(s, t)) {
            cur.assign(n, 0);
            ans += dfs(s, t, inf);
        }
        return ans;
    }
};
using Flow = Flow_<int>;
void solve() {
    int n, m;
    i64 c, d;
    cin >> n >> m >> c >> d;
    vector<string> a(n);
    for (int i = 0; i < n; i++) cin >> a[i];
    int cnt = 0;
    Flow flow(n + m + 2);
    int s = 0, t = n + m + 1;
    for (int j = 0; j < n; j++) {
        for (int k = 0; k < m; k++) {
            if (a[j][k] == '.') {
                flow.add(j + 1, k + n + 1, 1);
                cnt++;
            }
        }
    }
    i64 ans = cnt * d;
    for (int i = 1; i <= max(n, m); i++) {
        for (int j = 1; j <= n; j++) {
            flow.add(s, j, 1);
        }
        for (int j = 1; j <= m; j++) {
            flow.add(j + n, t, 1);
        }
        int cur = flow.work(s, t);
        cnt -= cur;
        ans = min(ans, 1ll * cnt * d + 1ll * i * c);
    }
    cout << ans << '\n';
}
int main() {
    // ios::sync_with_stdio(0); cin.tie(0), cout.tie(0);
    int t = 1; 
    // cin >> t;
    while(t--) solve();
    return 0;
}