let is_composite_number m =
  let rec inner n =
    if n mod m = 0 then true
    else if n >= m then false
    else inner (n + 1)
  in 
  if m = 2 then false
  else inner 2

let solve n = 
  let rec inner m =
    if n - 100 <= m && m <= n + 100 then
      begin
        if is_composite_number m then m
        else inner (m + 1)
      end
    else assert false
  in print_int @@ inner (n - 100)

let _ =
  let n = int_of_string @@ read_line () in
  solve n