#include <bits/stdc++.h>


#define N 600
#define INF 1e9
#define ll long long
using namespace std;



struct MF {
  struct edge {
    int v, nxt, cap, flow;
  } e[N];

  int fir[N], cnt = 0;

  int n, S, T;
  ll maxflow = 0;
  int dep[N], cur[N];

  void init(int nn, int s, int t) {
    memset(fir, -1, sizeof fir);
    cnt = 0; maxflow = 0;
    n = nn, S = s, T = t;
  }

  void addedge(int u, int v, int w) {
    e[cnt] = {v, fir[u], w, 0};
    fir[u] = cnt++;
    e[cnt] = {u, fir[v], 0, 0};
    fir[v] = cnt++;
  }

  bool bfs() {
    queue<int> q;
    memset(dep, 0, sizeof(int) * (n + 1));

    dep[S] = 1;
    q.push(S);
    while (q.size()) {
      int u = q.front();
      q.pop();
      for (int i = fir[u]; ~i; i = e[i].nxt) {
        int v = e[i].v;
        if ((!dep[v]) && (e[i].cap > e[i].flow)) {
          dep[v] = dep[u] + 1;
          q.push(v);
        }
      }
    }
    return dep[T];
  }

  int dfs(int u, int flow) {
    if ((u == T) || (!flow)) return flow;

    int ret = 0;
    for (int& i = cur[u]; ~i; i = e[i].nxt) {
      int v = e[i].v, d;
      if ((dep[v] == dep[u] + 1) &&
          (d = dfs(v, min(flow - ret, e[i].cap - e[i].flow)))) {
        ret += d;
        e[i].flow += d;
        e[i ^ 1].flow -= d;
        if (ret == flow) return ret;
      }
    }
    return ret;
  }

  void dinic() {
    while (bfs()) {
      memcpy(cur, fir, sizeof(int) * (n + 1));
      maxflow += dfs(S, INF);
    }
  }
} mf;

int n, m;
long long c, d, ans = 1e15, sum, num;
string s[N];
int h[N], l[N];

void work(int k) {
    mf.init(n + m + 2, 0, n + m + 1);
    for(int i = 1;i <= n; i++) {
        if(h[i] > k)
        for(int j = 1; j <= m; j++) 
            if(l[i] > k) mf.addedge(i, n + j, 1); 
    }
    for(int i = 1;i <= n; i++) 
        if(h[i] > k) mf.addedge(0, i, h[i] - k), num += h[i] - k;
    for(int i = 1;i <= m; i++) 
        if(l[i] > k) mf.addedge(n + i, n + m + 1, l[i] - k), num += l[i] - k;
    mf.dinic();
    num = num - mf.maxflow;
    sum = c * k + d * num;
}
int main() {
    cin>>n>>m>>c>>d;
    for(int i = 1;i <= n; i++) {
        cin>>s[i]; s[i] = " " + s[i];
        for(int j = 1; j <= m; j++) {
            if(s[i][j] == '.') h[i]++;
        }
    }
    for(int i = 1;i <= m; i++) 
        for(int j = 1; j <= n; j++) 
            if(s[j][i] == '.') l[i]++;

    for(int i = 0;i <= max(n, m); i++) {
        sum  = 0; num = 0; work(i);
        ans = min(ans, sum);
    } 
    cout<<ans<<endl;
    return 0;
}