const max=100000;
var v:array[1..max] of longint;
    i,j,n,c:longint;
begin
assign(input,'ciur.in');reset(input);
assign(output,'ciur.out');rewrite(output);
readln(n);
for i:=2 to trunc(sqrt(n)) do
  if v[i]=0 then
   for j:=2 to max div i do
    v[i*j]:=1;
for i:=2 to n do
 if v[i]=0 then inc(c);
write(c);
close(input);close(output);
end.