var
 fa:array[0..100010]of longint;
 n,i,j,a,b,ans:longint;
function find(x:longint):longint;
 begin
  if fa[x]=x then exit(x);
  fa[x]:=find(fa[x]);
  exit(fa[x]);
 end;
procedure hebing(x,y:longint);
 var i,j:longint;
 begin
  i:=find(x);
  j:=find(y);
  if i=j then
   begin inc(ans);exit;end;
  fa[i]:=j;
 end;
begin
assign(input,'explosion.in');reset(input);
assign(output,'explosion.out');rewrite(output);
 for i:=0 to 100010 do fa[i]:=i;
 ans:=0;
 read(a);
 while (a<>-1) do
  begin
   readln(b);
   hebing(a,b);
   read(a);
  end;
 writeln(ans);
close(input);close(output);
end.