{ tde }
{$APPTYPE CONSOLE}
{$B-,R-,O+}
const
 maxn=1000;
var
 fi,fo:text;
 n,i,tek,groups:smallint;
 f:array[0..maxn] of smallint;
begin
 assign(fi,'liars.dat');
 assign(fo,'liars.sol');
 reset(fi);
 rewrite(fo);
 readln(fi,n);
 fillchar(f,sizeof(f),0);
 for i:=1 to n do
  begin
   read(fi,tek);
   f[tek]:=f[tek]+1;
  end;
 groups:=0;
 for i:=1 to n do
  if(f[i]=i)then
   groups:=groups+1;;

 if(groups=1)then
  writeln(fo,0) else
  writeln(fo,groups);
 close(fi);
 close(fo);
end.