#include <bits/stdc++.h>
#define rep(x, l, r) for(int x = l; x <= r; x++)
#define int long long 
using namespace std;

const int INF = 1e14;
const int MAXN = 1e4 + 5;
const int MAXM = 3e6 + 5;
queue<int> que;
int S, T, cnt, mincost;
int head[MAXN], cur[MAXN], nxt[MAXM], to[MAXM], value[MAXM], cost[MAXM];
int dep[MAXN],  s[MAXN], E[MAXN];
char st[MAXN];


void init(){
    cnt = 0;
    rep(i, S, T) head[i] = -1;
}

void add(int u, int v, int w){
    nxt[cnt] = head[u];
    head[u] = cnt;
    to[cnt] = v;
    value[cnt] = w;
    cnt++;
}

void addedge(int u, int v, int w){
    add(u, v, w);
    add(v, u, 0);
}

bool bfs(){
    while(!que.empty()) que.pop();
    rep(i, S, T) dep[i] = 0;
    que.push(S);
    dep[S] = 1;
    while(!que.empty()){
        int u = que.front();
        que.pop();
        for(int e = head[u]; e != -1; e = nxt[e]){
            int v = to[e];
            if(dep[v] || !value[e]) continue;
            dep[v] = dep[u] + 1;
            que.push(v);
        }
    }
    return dep[T];
}

int dfs(int u, int flow){
    if(u == T) return flow;
    for(int& e = cur[u]; e != -1; e = nxt[e]){
        int v = to[e];
        if(!value[e] || dep[v] != dep[u] + 1) continue;
        int q = dfs(v, min(flow, value[e]));
        if(q){
            value[e] -= q;
            value[e ^ 1] += q;
            return q;
        }
    }
    return 0;
}

int dinic(){
    int ans = 0;
    while(bfs()){
        rep(i, S, T) cur[i] = head[i];
        while(int d = dfs(S, INF)) ans += d;
    }
    return ans;
}

signed main(){
    int n, m, c, d;
    scanf("%lld%lld%lld%lld", &n, &m, &c, &d);
    S = 0, T = n + m + 1;
    init();
    int res = 0;
    rep(i, 1, n){
        scanf("%s", st);
        rep(j, 1, m){
            if(st[j - 1] == '.'){
                addedge(i, n + j, 1);
                res++;
                s[i]++;
                s[n + j]++;
            }
        }
    }
    int mx = 0;
    rep(i, 1, n){
        mx = max(mx, s[i]);
        E[i] = cnt;
        addedge(S, i, 0);
    }
    rep(i, 1, m){
        mx = max(mx, s[n + i]);
        E[n + i] = cnt;
        addedge(n + i, T, 0);
    }
    int ans = res * d;
    // printf("%d\n", ans);
    rep(i, 1, mx){
        rep(i, 1, n + m){
            value[E[i]]++;
        }
        res -= dinic();
        
        ans = min(ans, i * c + res * d);
    }
    printf("%lld\n", ans);
    return 0;
}