var f:text;
    v:array[1..2000000] of boolean;
    i,j,prim,n:longint;

begin
 assign(f,'ciur.in');
 reset(f);
 readln(f,n);
 close(f);

 i:=3;
 prim:=1;
 while i<=n  do begin
   if not v[i] then begin
      inc(prim);
      j:=i;
      while j<=n do begin
         v[j]:=true;
         inc(j,i);
      end;
   end;
   inc(i,2);
 end;

 assign(f,'ciur.out');
 rewrite(f);
 writeln(f,prim);
 close(f);

end.