var a:array[1..2000000]of boolean;
    n,k,i,j:longint;f:text;
begin
 assign(f,'ciur.in');
 reset(f);
 readln(f,n);
 close(f);
 for i:=1 to n do a[i]:=true;
 a[1]:=false; k:=0;
 for i:=1 to n do
  if a[i] then
   begin
    j:=i*2;
    while j<=n do
     begin
      a[j]:=false;
      j:=j+i;
     end;
    inc(k);
   end;
 assign(f,'ciur.out');
 rewrite(f);
 writeln(f,k);
 close(f);
end.