#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
// #define int long long
#define QF ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)

constexpr int N = 1e5 + 10;
constexpr int M = 1e5 + 10;
const int inf = 1e9;
int n, m, s, t, tot = 1, ans;
int head[N], now[N], dep[N];
bool used[N];
string st[N];
struct edge
{
    int v, w, nxt;
} edges[M << 1];

void add(int u, int v, int w)
{
    edges[++tot] = {v, w, head[u]};
    head[u] = tot;
}
void addedge(int u, int v, int w)
{
    used[u] = true;
    used[v] = true;
    add(u, v, w);
    add(v, u, 0);
}
bool bfs()
{
    memset(dep, 0, sizeof(dep));
    queue<int> q;
    q.push(s);
    dep[s] = 1;
    while (!q.empty())
    {
        auto u = q.front();
        q.pop();
        for (int i = head[u]; i; i = edges[i].nxt)
        {
            auto [v, w, x] = edges[i];
            if (w && !dep[v])
            {
                dep[v] = dep[u] + 1;
                q.push(v);
                if (v == t)
                    return true;
            }
        }
    }
    return false;
}
int dfs(int u, int flow)
{
    if (u == t)
    {
        return flow;
    }
    int res = 0;
    for (int i = now[u]; i && flow; i = edges[i].nxt)
    {
        now[u] = i;
        auto [v, w, x] = edges[i];
        if (w && dep[v] == dep[u] + 1)
        {
            int k = dfs(v, min(flow, w));
            if (!k)
            {
                dep[v] = 0;
            }
            res += k;
            flow -= k;
            edges[i].w -= k;
            edges[i ^ 1].w += k;
        }
    }
    return res;
}
void clear()
{
    tot = 1;
    memset(head, 0, sizeof(head));
    memset(used, 0, sizeof(used));
    s = 0, t = 0;
}
void solve()
{
    int c, d;
    cin >> n >> m >> c >> d;
    for (int i = 1; i <= n; i++)
    {
        cin >> st[i];
        st[i] = " " + st[i];
    }
    s = 1e5, t = s + 1;
    int all = 0;
    for (int j = 1; j <= n; j++)
    {
        addedge(s, j, 1);
        for (int i = 1; i <= m; i++)
        {
            if (st[j][i] != '*')
            {
                addedge(j, i + n, 1);
                all++;
            }
        }
    }
    for (int j = 1; j <= m; j++)
    {
        addedge(j + n, t, 1);
    }
    int minn = inf;
    ans = 0;
    while (bfs())
    {
        for (int i = 1; i <= n + m; i++)
        {
            now[i] = head[i];
        }
        now[s] = head[s];
        now[t] = head[t];
        ans += dfs(s, inf);
    }
    int nx = c + (all - ans) * d;
    minn = nx;
    for (int i = 2; i <= max(n, m); i++)
    {
        for (int x = head[s]; x; x = edges[x].nxt)
        {
            edges[x].w++;
        }
        for (int x = head[t]; x; x = edges[x].nxt)
        {
            edges[x ^ 1].w++;
        }
        while (bfs())
        {
            for (int w = 1; w <= n + m; w++)
            {
                now[w] = head[w];
            }
            now[s] = head[s];
            now[t] = head[t];
            ans += dfs(s, inf);
        }
        // cout << ans << endl;
        nx = i * c + (all - ans) * d;
        minn = min(minn, nx);
    }
    cout << minn << endl;
}
signed main()
{
    QF;
    int T = 1;
    for (int i = 1; i <= T; i++)
    {
        solve();
    }
}