ssss

#include <vector>
#include <iostream>
#include <math.h>
#include <algorithm>
#include <map>
#include <set>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>

std::vector<std::vector<int>> g;
std::vector<bool> used;
std::vector<bool> covered;
std::vector<int> match;

bool try_kunn(int v) {
    used[v] = true;
    for (auto u : g[v])
        if (match[u] == -1 || (!used[match[u]] && try_kunn(match[u]))) {
            match[u] = v;
            return true;
        }
    return false;
}

int main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    std::iostream::ios_base::sync_with_stdio(0);
    std::cin.tie(0);
    std::cout.tie(0);
    int n, m, a, b;
    std::cin >> n >> m >> a >> b;
    std::vector<std::vector<char>> floor(n + 2, std::vector<char>(m + 2, '*'));
    int cnt = 0;
    for (int i = 1; i < n + 1; i++) {
        for (int j = 1; j < m + 1; j++) {
            std::cin >> floor[i][j];
            if (floor[i][j] == '.')
                cnt++;
        }
    }
    if (b * 2 <= a) {
        std::cout << b * cnt;
        return 0;
    }
    g.resize(n * m);
    std::vector<int> move_x = {0, 1, 1, 1, 0, -1, -1, -1};
    std::vector<int> move_y = {1, 1, 0, -1, -1, -1, 0, 1};
    for (int i = 1; i < n + 1; i++)
        for (int j = 1; j < m + 1; j++)
            if (floor[i][j] == '.')
                for (int k = 0; k < 8; k++)
                    if (floor[i + move_x[k]][j + move_y[k]] == '.')
                        g[(i - 1) * m + (j - 1)].push_back((i - 1 + move_x[k]) * m + (j - 1 + move_y[k]));
    used.resize(n * m);
    covered.resize(n * m);
    match.resize(n * m, -1);
    bool flag = true;
    while (flag) {
        used.assign(n * m, false);
        flag = false;
        for (int i = 0; i < n * m; i++)
            if (!covered[i] && try_kunn(i)) {
                covered[i] = true;
                flag = true;
            }
    }
    int par_cnt = 0;
    for (int i = 0; i < n * m; i++) {
        if (match[i] != -1)
            par_cnt += 1;
    }
    std::cout << (par_cnt / 2) * a + (cnt - par_cnt) * b;
    return 0;
}