program ciurul;
var f,g:text;
    a:array[1..2000001] of boolean;
     k,i,n,j:longint;
begin
assign(f,'ciur.in'); reset(f); readln(f,n);  close(f);
assign(g,'ciur.out'); rewrite(g);
for i:=2 to n do a[i]:=true;
for i:=2 to n do
  if a[i] then begin
          j:=i;  inc(k);
          while j<=n do begin
            a[j]:=false;
            j:=j+i;
            end;
          end;
  writeln(g,k);
  close(g);
end.