#include <bits/stdc++.h>
using namespace std;
int h , w , d , r , cnt , dis[2005][2005];
char c[2005][2005];
bool vis[2005][1005] , go[2005][2005];
struct node{
    int x , y;
    bool type;
    //type 是否吃魔药
    //0 没有 1 吃了
};
int dx[4] = {0 , 0 , 1 , -1} , dy[4] = {1 , -1 , 0 , 0};
bool range_point(int x , int y){
    if(x < 1 || y < 1) return 0;
    if(x > h || y > w) return 0;
    return 1;
}
void flood_file(int sx , int sy){
	queue <node> q;
	q.push((node){sx , sy , 0});
	while(!q.empty()){
		node now = q.front();
		q.pop();
		int x = now.x , y = now.y;
		for(int i = 0; i < 4; i++){
			int nx = x + dx[i] , ny = y + dy[i];
			if(range_point(nx , ny) && !vis[nx][ny] && c[nx][ny] == '.'){
				q.push((node){nx , ny , 0});
				vis[nx][ny] = true;
			}
		}
	}
	return;
}
void Bfs(){
	queue <node> q;
	go[1][1] = true;
	q.push((node){1 , 1 , 0});
	while(!q.empty()){
		node now = q.front();
		q.pop();
		for(int i = 0; i < 4; i++){
            int nx = now.x + dx[i];
            int ny = now.y + dy[i];
            if(range_point(nx , ny) && !go[nx][ny] && c[nx][ny] == '.'){
                go[nx][ny] = true;
                q.push((node){nx , ny , 0});
            }
        }
	}
	return;
}
void bfs(){
    queue <node> q;
    memset(dis , -1 , sizeof(dis));
    dis[1][1] = 0;
    q.push((node){1 , 1 , 0});
    while(!q.empty()){
        node now = q.front();
        q.pop();
        if(now.x == h && now.y == w){
            cout << dis[h][w];
            return;
        }
        for(int i = 0; i < 4; i++){
            int nx = now.x + dx[i];
            int ny = now.y + dy[i];
            if(range_point(nx , ny) && dis[nx][ny] == -1 && c[nx][ny] == '.'){
                dis[nx][ny] = dis[now.x][now.y] + 1;
                q.push((node){nx , ny , now.type});
            }
        }
        bool type = now.type;
        int nx = now.x + d;
        int ny = now.y + r;
        if(!type && (!go[nx][ny] || cnt == 1) && (d >= 0 || r >= 0)){
            if(range_point(nx , ny) && dis[nx][ny] == -1 && c[nx][ny] == '.'){
                dis[nx][ny] = dis[now.x][now.y] + 1;
                q.push((node){nx , ny , 1});
            }
        }
    }
    cout << -1;
    return;
}
int main(){
    cin >> h >> w >> d >> r;
    for(int i = 1; i <= h; i++)
        for(int j = 1; j <= w; j++)
            cin >> c[i][j];
    for(int i = 1; i <= h; i++){
    	for(int j = 1; j <= w; j++){
    		if(c[i][j] == '.' && !vis[i][j]){
    			flood_file(i , j);
    			vis[i][j] = true;
    			cnt++;
    		}
    	}
    }
    Bfs();
    bfs();
    return 0;
}