program sieve;
var f,g:text;
    a:array[2..20000000]of 0..1;
    n,i,j,b:longint;
begin
 assign(f,'ciur.in'); reset(f);
 assign(g,'ciur.out'); rewrite(g);
 readln(f,n);
 for i:=2 to n do
  if a[i]=0 then begin
   inc(b);
   for j:=i+1 to n do
    if (j mod i)=0 then a[j]:=1;
  end;
 writeln(g,b);
 close(f); close(g);
end.