Scanf.scanf "%d %d %d %d" (fun a b c d ->
    let a = [| a; b; c; d |] in
    Array.sort compare a;
    print_endline @@
        if a.(1) - a.(0) = 1 &&
           a.(2) - a.(1) = 1 &&
           a.(3) - a.(2) = 1 then "Yes" else "No"
)