Var f,g:text;
    v:array [1..2000000] of boolean;
    n,i,j,s,k:longint;

Begin
assign(f, 'ciur.in');reset(f);
assign(g, 'ciur.out');rewrite(g);
read(f, n);
for i:=1 to n do
  v[i]:=true;
for i:=2 to trunc(sqrt(n)) do
  if v[i]=true then
    begin
      k:=0;
      repeat
         begin
          j:=i*i+k*i;
          v[j]:=false;
          inc(k);
        end;
      until j>=n;
    end;
for i:=2 to n do
  if v[i]=true then inc(s);
write(g, s);
close(f);
close(g);
End.