var a:array[1..2000000] of byte;
    i,j,n,k:longint;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
readln(f,n);
a[1]:=0;
for i:=2 to n do
  a[i]:=1;
for i:=2 to n do
  if a[i]=1 then
    begin
      k:=k+1;
      j:=i+i;
      while j<=n do
        begin
          a[j]:=0;
          j:=j+i;
        end;
    end;
writeln(g,k);
close(f);close(g);
end.