#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr int N = 500 + 5;
constexpr int M = 2e5 + 5;
struct flow {
  int cnt = 1, hd[N], nxt[M << 1], to[M << 1], lim[M << 1];
  void add(int u, int v, int w) {
    nxt[++cnt] = hd[u], hd[u] = cnt, to[cnt] = v, lim[cnt] = w;
    nxt[++cnt] = hd[v], hd[v] = cnt, to[cnt] = u, lim[cnt] = 0;
  }
  int T, cur[N], dis[N];
  int dfs(int id, int res) {
    if(id == T) return res;
    int flow = 0;
    for(int i = cur[id]; i && res; i = nxt[i]) {
      cur[id] = i;
      int it = to[i], c = min(lim[i], res);
      if(dis[id] + 1 == dis[it] && c) {
        int k = dfs(it, c);
        flow += k, res -= k;
        lim[i] -= k, lim[i ^ 1] += k;
      }
    }
    if(!flow) dis[id] = -1;
    return flow;
  }
  int maxflow(int s, int t) {
    T = t;
    int flow = 0;
    while(1) {
      queue<int> q;
      memset(dis, -1, N << 2);
      memcpy(cur, hd, N << 2);
      q.push(s), dis[s] = 0;
      while(!q.empty()) {
        int t = q.front();
        q.pop();
        for(int i = hd[t]; i; i = nxt[i]) {
          if(lim[i] && dis[to[i]] == -1) {
            dis[to[i]] = dis[t] + 1;
            q.push(to[i]);
          }
        }
      }
      if(dis[t] == -1) return flow;
      flow += dfs(s, 1e9);
    }
  }
} g;

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  ll n, m, c, d;
  cin >> n >> m >> c >> d;
  ll tot = 0, T = n + m + 1;
  for(int i = 1; i <= n; i++) g.add(0, i, 0);
  for(int i = 1; i <= m; i++) g.add(n + i, T, 0);
  for(int i = 1; i <= n; i++) {
    static char s[N];
    cin >> s + 1;
    for(int j = 1; j <= m; j++) {
      if(s[j] == '.') {
        g.add(i, n + j, 1);
        tot++;
      }
    }
  }
  ll flow = 0, ans = d * tot;
  for(int k = 1; k <= max(n, m); k++) {
    for(int i = 1; i <= n + m; i++) g.lim[i * 2]++;
    flow += g.maxflow(0, T);
    ans = min(ans, c * k + d * (tot - flow));
  }
  cout << ans << "\n";
  return 0;
}