#include<bits/stdc++.h>
using namespace std;
namespace dinic {
    const int N = 4e5 + 10;
    int n, now = 1, fst[N], nxt[N], num[N], T; long long wi[N];
    void add(int u, int v, long long w) {
        nxt[++now] = fst[u], fst[u] = now, num[now] = v, wi[now] = w;
        nxt[++now] = fst[v], fst[v] = now, num[now] = u; wi[now] = 0;
    }
    void clr() {
        for(int i = 1; i <= n; i++) fst[i] = 0;
        now = 1;
    }
    int dis[N], cur[N];
    int bfs(int s, int t) {
        for(int i = 1; i <= n; i++) dis[i] = -1, cur[i] = fst[i];
        dis[s] = 0; queue<int> q; q.push(s);
        while(!q.empty()) {
            int p = q.front(); q.pop();
            for(int i = fst[p]; i; i = nxt[i])
                if(wi[i] && dis[num[i]] == -1) {
                    dis[num[i]] = dis[p] + 1;
                    if(num[i] == t) return 1;
                    q.push(num[i]);
                }
        }
        return 0;
    }  
    long long dfs(int x, long long f) {
        if(x == T) return f;
        long long r = 0;
        for(int &i = cur[x]; i; i = nxt[i]) {
            if(!wi[i] || dis[num[i]] != dis[x] + 1) continue;
            long long t = dfs(num[i], min(f, wi[i]));
            r += t, f -= t;
            wi[i] -= t, wi[i ^ 1] += t;
            if(!f) return r;
        }
        return r;
    }
    const long long inf = 1e18;
    long long solve(int s, int t) {
        long long r = 0; T = t;
        while(bfs(s, t)) r += dfs(s, inf);
        return r;
    }
}
int n,m;
long long c,d;
int main()
{
    cin>>n>>m>>c>>d;
    long long ans=0;
    dinic::n=n+m+2;
    for(int i=1;i<=n;i++)
        dinic::add(n+m+1,i,1);
    for(int i=1;i<=m;i++)
        dinic::add(n+i,n+m+2,1);
    int tt=0;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
        {
            char c;
            cin>>c;
            if(c=='.'){
                dinic::add(i,j+n,1);
                // ans+=d;
                tt++;
            }
        }
    ans=tt*d;
    for(int i=1;i<=max(n,m);i++)
    {
        tt-=dinic::solve(n+m+1,n+m+2);
        // cerr<<tt<<endl;
        ans=min(ans,(tt)*d+i*c);
        for(int j=2;j<=(n+m)*2;j+=2)
            dinic::wi[j]++;
    }
    cout<<ans<<endl;
    return 0;
}