1 type node=record
 2        next,point:longint;
 3      end;
 4 var edge:array[0..1000010] of node;
 5     a:array[0..60,0..60] of longint;
 6     cx,cy,p:array[0..3000] of longint;
 7     dx,dy:array[1..4] of longint;
 8     v:array[0..3000] of boolean;
 9     t,len,ans,i,j,k,n,m,r,c,x,y:longint;
10     s:ansistring;
11
12 procedure add(x,y:longint);
13   begin
14     inc(len);
15     edge[len].point:=y;
16     edge[len].next:=p[x];
17     p[x]:=len;
18   end;
19
20 function find(x:longint):integer;
21   var i,y:longint;
22   begin
23     i:=p[x];
24     while i<>-1 do
25     begin
26       y:=edge[i].point;
27       if not v[y] then
28       begin
29         v[y]:=true;
30         if (cy[y]=-1) or (find(cy[y])=1) then
31         begin
32           cx[x]:=y;
33           cy[y]:=x;
34           exit(1);
35         end;
36       end;
37       i:=edge[i].next;
38     end;
39     exit(0);
40   end;
41
42 begin
43   readln(n,m,r,c);
44   for i:=1 to n do
45   begin
46     readln(s);
47     for j:=1 to m do
48     begin
49       if s[j]='.' then
50       begin
51         inc(t);
52         a[i,j]:=t;
53       end;
54     end;
55   end;
56   dx[1]:=r; dx[2]:=r; dx[3]:=c; dx[4]:=c;
57   dy[1]:=c; dy[2]:=-c; dy[3]:=r; dy[4]:=-r;
58   fillchar(p,sizeof(p),-1);
59   fillchar(cx,sizeof(cx),-1);
60   fillchar(cy,sizeof(cy),-1);
61   for i:=1 to n do
62     for j:=1 to m do
63       if a[i,j]<>0 then
64         for k:=1 to 4 do
65         begin
66           x:=i+dx[k];
67           y:=j+dy[k];
68           if (x<=n) and (y>0) and (y<=m) and (a[x,y]>0) then add(a[i,j],a[x,y]);
69         end;
70
71   for i:=1 to t do
72     if cx[i]=-1 then
73     begin
74       fillchar(v,sizeof(v),false);
75       ans:=ans+find(i);
76     end;
77   writeln(t-ans);
78 end.