#include <stdio.h>
#include <vector>
#include <cstdio>
#define MAX 102
using namespace std;


char s[MAX][MAX];
int res, n, m, a, b, i, j, c;
vector<vector<int> > g;
vector<int> mt, used, par;
int dfs(int v)
{
    if (used[v]) return 0;
    used[v] = 1;
    for (int i = 0; i < g[v].size(); i++)
    {
        int to = g[v][i];
        if (mt[to] == -1 || dfs(mt[to]))
        {
            mt[to] = v;
            par[v] = to;
            return 1;
        }
    }
    return 0;
}

void AugmentingPath(void)
{
    int i, j, run;
    mt.assign(n * m, -1);
    par.assign(n * m, -1);
    for (run = 1; run; )
    {
        run = 0; used.assign(n * m, 0);
        for (i = 0; i < n; i++)
            for (j = 0; j < m; j++)
            {
                if ((i + j) % 2) continue;
                if ((par[i * m + j] == -1) && dfs(i * m + j)) run = 1;
            }
    }
}

int main(void)
{
    int empty;
    scanf("%d %d %d %d\n", &n, &m, &a, &b);
    for (i = 0; i < n; i++) fgets(s[i], MAX, stdin);
    g.resize(n * m);
    empty = 0;
    for (i = 0; i < n; i++)
        for (j = 0; j < m; j++)
        {
            if (s[i][j] == '.') continue;
            empty++;
            if ((i + j) % 2) continue;
            int u = i * m + j;
            if (j && (s[i][j - 1] == '*')) g[u].push_back(u - 1);
            if ((j < m - 1) && (s[i][j + 1] == '*')) g[u].push_back(u + 1);
            if (i && (s[i - 1][j] == '*')) g[u].push_back(u - m);
            if ((i < n - 1) && (s[i + 1][j] == '*')) g[u].push_back(u + m);
        }
    if (2 * b <= a)
    {
        printf("%d\n", empty * b);
        return 0;
    }
    AugmentingPath();
    for (c = i = 0; i < n * m; i++)
        if (mt[i] != -1) c++;
    res = c * a + (empty - 2 * c) * b;
    printf("%d\n", res);
    return 0;
}