var
 fa:array[0..100011] of longint;
 i,j,m,n,x,y,ans:longint;
function get(v:longint):longint;
begin
 if fa[v]=-1 then get:=v else
  begin
   fa[v]:=get(fa[v]);
   get:=fa[v];
  end;
end;
procedure he(x,y:longint);
var i,j:longint;
begin
 i:=get(x);
 j:=get(y);
 fa[i]:=j;
end;
begin
 assign(input,'explosion.in');reset(input);
 assign(output,'explosion.out');rewrite(output);
 fillchar(fa,sizeof(fa),$ff);
 repeat
 read(x);
 if x=-1 then break;
 readln(y);
 if get(x)<>get(y) then
  begin
   he(x,y);
  end else inc(ans);
 until false;
 writeln(ans);
 close(input);close(output);
end.