let n = read_int ();;

if n = 1 then (
  print_endline "0";
  exit 0;
);;

let table = Array.make 500001 true;;
let sqtable = Array.make 500020 false;;

for i = 2 to 500000 do
  if table.(i) then (
    if i <= n && i * i <= 500020 then sqtable.(i*i) <- true;
    for j = 2 to 500000/i do
      table.(i*j) <- false
    done
  )
done;;

let ans = ref 1;;
for i = 3 to n do
  if table.(i) && sqtable.(i+2) then (
    ans := !ans + 2;
  );
done;;

Printf.printf "%d\n" !ans;;