#define debug(tl) cerr<<#tl<<' '<<tl<<'\n';
#include "bits/stdc++.h"
using namespace std;
#define all(mask) mask.begin(), mask.end()
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef long double ld;
const int MAXN = 1e4;
vector<int> gr[MAXN];
vector<int> used(MAXN), mpair(MAXN, -1);
bool kuhn(int v) {
    if (used[v]) return false;
    used[v] = true;
    for (auto u : gr[v]) {
        if (mpair[u] == -1 || kuhn(mpair[u])) {
            mpair[u] = v;
            return true;
        }
    }
    return false;
}
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    freopen("dominoes.in", "r", stdin);
    freopen("dominoes.out", "w", stdout);
    int n, m, a0, b0, cur = 0;
    cin >> n >> m >> a0 >> b0;
    vector<vector<char>> a(n + 1, vector<char>(m + 1, '.'));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> a[i][j];
            cur += a[i][j] == '*';
        }
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (a[i][j] == '*') {
                if ((i + j) % 2) {
                    if (a[i][j + 1] == '*') {
                        gr[i * m + j].push_back(i * m + 1 + j);
                    }
                    if (a[i + 1][j] == '*') {
                        gr[i * m + j].push_back(i * m + m + j);
                    }
                }
                else {
                    if (a[i][j + 1] == '*') {
                        gr[i * m + j + 1].push_back(i * m + j);
                    }
                    if (a[i + 1][j] == '*') {
                        gr[(i + 1) * m + j].push_back(i * m + j);
                    }
                }
            }
        }
    }
    for (int i = 0; i < MAXN; i++) {
        used.assign(MAXN, 0);
        kuhn(i);
    }
    int cnt = 0;
    for (int i = 0; i < MAXN; i++) {
        if (mpair[i] != -1) {
            cnt++;
        }
    }
    cout << min(cnt * a0 + cur * b0 - cnt * 2 * b0, b0 * cur);

}