#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first 
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const LL LINF = 1e18;

struct Graph
{
	struct Edge
	{
		int from, to;
		LL cap, flow;
	};
	
	int n;
	vector<Edge> edges;
	vector<VI> g;
	VI d, p;
	
	
	void init(int _n)
	{
		n = _n;
		edges.clear();
		g.clear();
		g.resize(n);
		d.resize(n);
		p.resize(n);
	}
	
	void addEdge(int from, int to, LL cap)
	{
		assert(0 <= from && from < n);
		assert(0 <= to && to < n);
		assert(0 <= cap);
		g[from].PB(SZ(edges));
		edges.PB({from, to, cap, 0});
		g[to].PB(SZ(edges));
		edges.PB({to, from, 0, 0});
	}
	int bfs(int s, int t)
	{
		fill(ALL(d), -1);
		d[s] = 0;
		queue<int> q;
		q.push(s);
		while (!q.empty())
		{
			int v = q.front();
			q.pop();
			for (int e : g[v])
			{
				int to = edges[e].to;
				if (edges[e].flow < edges[e].cap && d[to] == -1)
				{
					d[to] = d[v] + 1;
					q.push(to);
				}
			}
		}
		return d[t];
	}
	LL dfs(int v, int t, LL flow)
	{
		if (v == t || flow == 0)
			return flow;
		for (; p[v] < SZ(g[v]); p[v]++)
		{
			int e = g[v][p[v]], to = edges[e].to;
			LL c = edges[e].cap, f = edges[e].flow;
			if (f < c && (to == t || d[to] == d[v] + 1))
			{
				LL push = dfs(to, t, min(flow, c - f));
				if (push > 0)
				{
					edges[e].flow += push;
					edges[e ^ 1].flow -= push;
					return push;
				}
			}
		}
		return 0;
	}
	LL flow(int s, int t)
	{
		assert(0 <= s && s < n);
		assert(0 <= t && t < n);
		assert(s != t);
		LL flow = 0;
		while (bfs(s, t) != -1)
		{
			fill(ALL(p), 0);
			while (true)
			{
				LL f = dfs(s, t, LINF);
				if (f == 0)
					break;
				flow += f;
			}
		}
		return flow;
	}
};

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int n, m;
	cin >> n >> m;
	int a, b;
	cin >> a >> b;
	vector<string> v(n);
	FOR (i, 0, n)
	{
		cin >> v[i];
	}
	int s = n * m;
	int t = s + 1;
	Graph g;
	g.init(n * m + 2);
	FOR (i, 0, n)
	{
		FOR (j, 0, m)
		{
			int idx = i * m + j;
			if (v[i][j] == '.')
				g.addEdge(s, idx, b);
			else
				g.addEdge(idx, t, b);
			if (i + 1 < n)
			{
				g.addEdge(idx, idx + m, a);
				g.addEdge(idx + m, idx, a);
			}
			if (j + 1 < m)
			{
				g.addEdge(idx, idx + 1, a);
				g.addEdge(idx + 1, idx, a);
			}
		}
	}
	
	cout << g.flow(s, t) << '\n';
	
	return 0;
}