var
 a: array[1..20000] of boolean;
 i,j,n,r:longint;
 fin,fou:text;

begin
r:=0;
   assign(fin,'ciur.in');
   assign(fou,'ciur.out');
   reset(fin);
   rewrite(fou);
    read(fin,n);
     for i:=1 to n do a[i]:=true;
     for i:=2 to n do
      if a[i]=true then
       for j:=2 to n div i do
        a[i*j]:=false;
     for i:=1 to n do
       if a[i]=true then inc(r);
       write(fou,r);
    close(fin);
    close(fou);

end.