#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll INF = 1e18;
const int N = 510, M = 2e6 + 7;

int head[N], nex[M], ver[M], tot = 1;
ll edge[M];
int s, t, vnum;
ll maxflow;
ll deep[N];
int now[N];
queue<int> q;

inline void add(int x, int y, int z)
{
    ver[++tot] = y;
    edge[tot] = z;
    nex[tot] = head[x];
    head[x] = tot;
}

inline bool bfs()
{
    for (int i = 0; i <= vnum; i++)
        deep[i] = INF;
    while (!q.empty())
        q.pop();
    q.push(s);
    deep[s] = 0;
    now[s] = head[s];
    while (!q.empty())
    {
        int x = q.front();
        q.pop();
        for (int i = head[x]; i; i = nex[i])
        {
            int y = ver[i];
            if (edge[i] > 0 && deep[y] == INF)
            {
                q.push(y);
                now[y] = head[y];
                deep[y] = deep[x] + 1;
                if (y == t)
                    return 1;
            }
        }
    }
    return 0;
}

inline ll dfs(int x, ll flow)
{
    if (x == t)
        return flow;
    ll ans = 0, k, i;
    for (i = now[x]; i && flow; i = nex[i])
    {
        now[x] = i;
        int y = ver[i];
        if (edge[i] > 0 && (deep[y] == deep[x] + 1))
        {
            k = dfs(y, min(flow, edge[i]));
            if (!k)
                deep[y] = INF;
            edge[i] -= k;
            edge[i ^ 1] += k;
            ans += k;
            flow -= k;
        }
    }
    return ans;
}

void dinic()
{
    while (bfs())
        maxflow += dfs(s, INF);
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    ll n, m, c, d;
    cin >> n >> m >> c >> d;
    vector<string> g(n + 1);
    for (int i = 0; i < n; i++)
        cin >> g[i];

    ll blank = 0;
    for (int i = 0; i < n; i++)
    {
        ll cnt = 0;
        for (int j = 0; j < m; j++)
        {
            if (g[i][j] == '.')
            {
                blank++;

                add(i, n + j, 1);
                add(n + j, i, 0);
            }
        }
    }

    s = n + m, t = n + m + 1, vnum = n + m + 1;
    for (int i = n; i < n + m; i++)
    {
        add(i, t, n);
        add(t, i, 0);
    }

    ll res = d * blank;
    for (int k = 1; k <= max(n, m); k++)
    {
        for (int i = 0; i < n; i++)
        {
            add(s, i, 1);
            add(i, s, 0);
        }
        dinic();
        // cerr << k << " " << (blank - maxflow)  << '\n';
        res = min(res, c * k + d * (blank - maxflow));
    }

    cout << res << '\n';
    return 0;
}