Program p1;
var k,n : longint;
    f,g : text;
    p : array[1..2000000] of boolean;



Procedure ciur;
var i,j : longint;
begin
fillchar(p,sizeof(p),true);
 for i:=2 to n do
  if p[i] then
   begin
   inc(k);
   j:=2;
   while i*j<=n do
   begin
   p[i*j]:=false;
   inc(j);
   end;
   end;
end;










begin
assign(f,'ciur.in');
reset(f);
readln(f,n);
close(f);
k:=0;
ciur;
assign(g,'ciur.out');
rewrite(g);
writeln(g,k);
close(g);
end.