program ciur;
type vector=array [1..2000000] of boolean;
var f1,f2:text;
    v:vector;
    n,p,i,j:longint;
begin
assign(f1,'ciur.in');
reset(f1);
read(f1,n);
close(f1);
assign(f2,'ciur.out');
rewrite(f2);
p:=0;
for i:=2 to n do
  v[i]:=true;
for i:=2 to n  do
if v[i] then
  begin
    p:=p+1;
    for j:=2 to n div i do
      v[i*j]:=false;
  end;
write(f2,p);
close(f2);
end.