var v:array[1..2000000]of byte;
   i,j,n,nr:longint;

begin
  assign(input,'ciur.in'); reset(input);
  assign(output,'ciur.out'); rewrite(output);
   for i:=2 to 2000000 do
    if v[i]=0 then for j:=2 to 2000000 div i do v[i*j]:=1;
   readln(n);
   for i:=2 to n do if v[i]=0 then inc(nr);
   writeln(nr);
  close(input); close(output);
end.