const maxn=2000001;
var
 a: array[1..MaxN] of boolean;
 i,j,n,r:0..maxn;

begin
r:=0;
   assign(input,'ciur.in');  reset(input);
   assign(output,'ciur.out');  rewrite(output);
      read(input,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:=2 to n do
       if a[i]=true then inc(r);
       write(output,r);
    close(input);
    close(output);

end.