#include<bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define rin register int
const ll inf = 1145141919810;
using namespace std;
struct Dinic {
    int tp, s, t, n, m;
	struct Edge {int u, v; ll cap;};
    vector<ll> dis;
	vector<int> cur, que;
    vector<vector<int>> v;
    vector<Edge> e, _e;
    Dinic(int _n, int _s, int _t) {
        n = _n, s = _s, t = _t;
        dis.resize(_n + 1), cur.resize(_n + 1), que.resize(_n + 1), v.resize(n + 1);
    }

    void add(int x, int y, ll w) { _e.push_back({x, y, w});}
    void Add(int x, int y, int flw) {
        e.push_back(Edge {x, y, flw}), e.push_back(Edge {y, x, 0});
        v[x].push_back(e.size() - 2);
    }
    int bfs() {
        dis.assign(n + 1, inf);
        int l = 1, r = 1;
        que[1] = s, dis[s] = 0;
        while (l <= r) {
            int p = que[l++], to;
            for (int i: v[p])
                if (e[i].cap && dis[to = e[i].v] >= inf)
                    dis[to] = dis[p] + 1, que[++r] = to;
        }
        return dis[t] < inf;
    }
    int dfs(int p, ll a) {
        if (p == t || !a) return a;
        int sf = 0, flw;
        for (int &i = cur[p], to; i < (int) v[p].size(); ++i) {
            Edge &E = e[v[p][i]];
            if (dis[to = E.v] == dis[p] + 1 && (flw = dfs(to, min(a, E.cap)))) {
                E.cap -= flw;
                e[v[p][i] ^ 1].cap += flw;
                a -= flw;
                sf += flw;
                if (!a) break;
            }
        }
        return sf;
    }
    ll dinic(int tp = 1) {
        this -> tp = tp;
        int flw = 0;
        while (bfs()) cur.assign(n + 1, 0), flw += dfs(s, inf);
        return flw;
    }
    ll get_ans() {
        ll ans = 0;
        m = _e.size();
        sort(_e.begin(), _e.end(), [](Edge a, Edge b) { return a.cap > b.cap;});
        for(int rp = 0; rp <= 1; ++rp) for (int p = 1 << 30, i = 0; p; p /= 2) {
            for (;i < m && _e[i].cap >= p; ++i) 
                if (rp) v[_e[i].v].push_back(i * 2 + 1);
                else Add(_e[i].u, _e[i].v, _e[i].cap);
            ans += dinic(rp);
        }
        return ans;
    }
};

void slv(){
    ll n, m, C, D;
    cin >> n >> m >> C >> D;
    vector<string> s(n);


    for(int i = 0; i < n; ++i) cin >> s[i];

    ll ans = inf;
    for(ll k = 0; k <= max(n, m); ++k){
        ll a = 0;
        Dinic d(m + n + 2, m + n + 1, m + n + 2);
        for(int i = 1; i <= n; ++i) d.add(d.s, i, k);
        for(int i = 1; i <= m; ++i) d.add(i + n, d.t, k);
        for(int i = 1; i <= n; ++i){
            for(int j = 1; j <= m; ++j){
                if(s[i - 1][j - 1] == '.') d.add(i, j + n, 1);
                else a++;
            }
        }

        ll _ans = d.get_ans();
        ll z = n * m - a - _ans;
        ans = min(ans, C * k + D * z);
    }
    cout << ans << endl;
}


int main(){
    ios::sync_with_stdio(0), cin.tie(0);
    int _ = 1;
    //cin >> _;
    while(_--) slv();
    return 0;
}