#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <cctype>
#include <vector>
#include <cmath>
#include <queue>
using namespace std;
#define ll long long
#define mp make_pair
#define pii pair<int,int>
const int M = 2e5 + 10;
const int N = 510;
//n*m+n+m
struct edge {
    int to;
    int cap;
}e[M];

int n,m,s,t,cnt = -1;
vector <int> g[N];
int cur[N],h[N];
bool vis[N];

bool bfs(int s,int t) {
    for (int i = 1;i <= n+m+2;++i) h[i] = -1;
    //h.assign(2*n+10,-1);
    queue <int> que;
    h[s] = 0;
    que.push(s);
    while (!que.empty()) {
        const int u = que.front();
        que.pop();
        for (int i : g[u]) {
            auto [v,c] = e[i];
            if (c > 0 && h[v] == -1) {
                h[v] = h[u] + 1;
                if (v == t) return 1;
                que.push(v);
            }
        }
    }
    return false;
}

int dfs(int u,int t,int f) {
    if (u == t) {
        return f;
    }
    auto r = f;
    for (int &i = cur[u];i < int(g[u].size());++i) {
        const int j = g[u][i];
        auto [v,c] = e[j];
        if (c > 0 && h[v] == h[u] + 1) {
            auto a = dfs(v,t,min(r,c));
            e[j].cap -= a;
            e[j^1].cap += a;
            r -= a;
            if (!r) return f;
        }
    }
    return f - r;
}

void addedge(int u,int v,int c) {
    g[u].push_back(++cnt);
    e[cnt].to = v,e[cnt].cap = c;
    g[v].push_back(++cnt);
    e[cnt].to = u,e[cnt].cap = 0;
}

int maxflow() {
    int ans = 0;
    while (bfs(s,t)) {
        for (int i = 1;i <= n + m + 2;++i) cur[i] = 0; 
        //cout << ans << "\n";
        ans += dfs(s,t,numeric_limits<int>::max());
    }
    return ans;
}

ll c,d;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin >> n >> m >> c >> d;
	ll ans = 0,cnt = 0;
	for (int i = 1;i <= n;++i) {
		for (int j = 1;j <= m;++j) {
			char c;cin >> c;
			if (c == '.') {
				addedge(i,j+n,1);
				++cnt;
			}
		}
	}
	s = n + m + 1,t = n + m + 2;
	for (int i = 1;i <= n;++i) {
		addedge(s,i,0);
	}
	for (int i = 1;i <= m;++i) {
		addedge(n + i,t,0);
	}
	ans = d * cnt;
	ll res = 0;
	for (int k = 1;k <= cnt;++k) {
        for (int i : g[s]) {
            auto [v,c] = e[i];
			e[i].cap++;
		}
        for (int i : g[t]) {
            auto [v,c] = e[i];
			e[i^1].cap++;
		}
		ll now = maxflow();
		res += now;
		//cout << k << ":" << now << "\n";
		ans = min(ans,c * k + d * (cnt - res));
		if (res == cnt) break;
	}
	cout << ans;
	return 0;
}