求森林数，裸的并查集

Program c;
var
   n,i,j,ans:longint;
   map:array[1..100,1..2] of longint;
   f:array[1..100] of longint;
function getfather(a:longint):longint;
begin
   if f[a]=a then exit(a);
   f[a]:=getfather(f[a]);
   exit(f[a]);
end;
procedure union(a,b:longint);
begin
   f[getfather(a)]:=f[getfather(b)];
end;
begin
   read(n);
   for i:=1 to n do
   begin
      f[i]:=i;
      read(map[i,1],map[i,2]);
      for j:=1 to i-1 do
         if (map[i,1]=map[j,1]) or (map[i,2]=map[j,2]) then
            union(i,j);

   end;
   ans:=0;
   for i:=2 to n do
      if getfather(i)<>getfather(i-1) then
      begin
         inc(ans);
         union(i,i-1);
      end;
   writeln(ans);

end.