#include <bits/stdc++.h>
using namespace std;

#define fec(i, x, y) (int i = head[x], y = g[i].to; i; i = g[i].ne, y = g[i].to)
#define dbg(...) fprintf(stderr, __VA_ARGS__)
#define fi first
#define se second

using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;

template <typename A, typename B>
bool smax(A &a, const B &b) { return a < b ? a = b, 1 : 0; }
template <typename A, typename B>
bool smin(A &a, const B &b) { return b < a ? a = b, 1 : 0; }

constexpr int N = 250 * 2 + 2 + 7;
constexpr int M = 250 * 250 + 250 * 2 + 7;
constexpr int INF = INT_MAX;

int n, m, S, T, nod;
char s[N][N];
int sc[N], cl[N];

struct Edge
{
    int to, ne, f;
} g[M << 1];
int head[N], tot = 1;
void addedge(int x, int y, int z)
{
    g[++tot].to = y;
    g[tot].f = z;
    g[tot].ne = head[x];
    head[x] = tot;
}
void adde(int x, int y, int z)
{
    addedge(x, y, z);
    addedge(y, x, 0);
}

int dis[N], gap[N], cur[N], q[N];
void bfs()
{
    int hd = 0, tl = 0;
    q[++tl] = T, ++gap[dis[T] = 1];
    while (hd < tl)
    {
        int x = q[++hd];
        for
            fec(i, x, y) if (!dis[y] && g[i ^ 1].f) dis[y] = dis[x] + 1, ++gap[dis[y]], q[++tl] = y;
    }
}
int dfs(int x, int a)
{
    if (x == T || !a)
        return a;
    int flow = 0, f;
    for (int &i = cur[x]; i; i = g[i].ne)
        if (dis[x] == dis[g[i].to] + 1 && (f = dfs(g[i].to, std::min(a, g[i].f))))
        {
            g[i].f -= f, g[i ^ 1].f += f;
            a -= f, flow += f;
            if (!a)
                return flow;
        }
    --gap[dis[x]];
    if (!gap[dis[x]])
        dis[S] = nod + 1;
    ++gap[++dis[x]];
    return flow;
}
int ISAP()
{
    static int ans = 0;
    bfs();
    while (dis[S] <= nod)
        memcpy(cur + 1, head + 1, sizeof(*head) * nod), ans += dfs(S, INF);
    return ans;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr), cout.tie(nullptr);

    int c, d, mxk = 0, sum = 0;
    cin >> n >> m >> c >> d;
    for (int i = 1; i <= n; ++i)
    {
        cin >> (s[i] + 1);
        for (int j = 1; j <= m; ++j)
            s[i][j] = s[i][j] == '.', sc[i] += s[i][j], cl[j] += s[i][j], smax(mxk, cl[j]);
        smax(mxk, sc[i]), sum += sc[i];
    }

    S = n + m + 1, T = nod = S + 1;
    for (int i = 1; i <= n; ++i)
        adde(S, i, 0);
    for (int i = 1; i <= m; ++i)
        adde(i + n, T, 0);
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            if (s[i][j])
                adde(i, j + n, 1);

    ll ans = LLONG_MAX;
    for (int k = 0; k <= mxk; ++k)
    {
        if (k)
        {
            memset(gap + 1, 0, sizeof(*gap) * nod);
            memset(dis + 1, 0, sizeof(*dis) * nod);
            for (int i = 1; i <= n; ++i)
                ++g[i * 2].f;
            for (int i = 1; i <= m; ++i)
                ++g[(i + n) * 2].f;
        }
        smin(ans, (ll)c * k + (ll)d * (sum - ISAP()));
    }
    cout << ans << '\n';

    return 0;
}