let vsota_lihih_42 =
  let v = ref 0 in
  let i = ref 0 in
  while !i < 42 do
    v := !v + (2 * !i + 1) ;
    i := !i + 1
  done ;
  !v

let vsota_lihih1 n =
  let v = ref 0 in
  let i = ref 0 in
  while !i < n do
    v := !v + (2 * !i + 1) ;
    i := !i + 1
  done ;
  !v

let vsota_lihih2 n =
  let rec vsota v i =
    if i < n then
      vsota (v + (2 * i + 1))  (i + 1)
    else
      v
  in
  vsota 0 0

let vsota1 n =
  let v = ref 0 in
  let i = ref 1 in
  while !i <= n do
    v := !v + !i ;
    i := !i + 1
  done ;
  !v

let rec vsota2 = function
  | 0 -> 0
  | n -> n + vsota2 (n-1)

let vsota3 n =
  let rec vsota v i =
    if i <= n then
      vsota (v + i) (i + 1)
    else
      v
  in
  vsota 0 0

let fibonacci1 n =
  let a = ref 0 in
  let b = ref 1 in
  let i = ref 0 in
  while !i < n do
    let b' = !a + !b in
    a := !b ;
    b := b' ;
    incr i
  done ;
  !a

let rec fibonacci2 = function
  | 0 -> 0
  | 1 -> 1
  | n -> fibonacci2 (n-1) + fibonacci2 (n-2)

let fibonacci3 n =
  let rec fib a b i =
    if i < n then
      fib b (a + b) (i + 1)
    else
      a
  in
  fib 0 1 0

let zanka s0 p f r =
  let rec loop s =
    if p s then loop (f s) else r s
  in
  loop s0

let vsota4 n =
  zanka
    (0, 0)
    (fun (_, i) -> i <= n)
    (fun (v, i) -> (v+i, i+1))
    (fun (v, _) -> v)

let fibonacci4 n =
  zanka
    (0, 1, 0)
    (fun (_, _, i) -> i < n)
    (fun (a, b, i) -> (b, a+b, i+1))
    (fun (a, _, _) -> a)

let forzanka s0 a b f r =
    let rec loop s i =
        if i > b then
            r s
        else
            loop (f i s) (i+1)
    in
    loop s0 a

let fibonacci5 n =
    forzanka (0, 1) 1 n
        (fun (a,b) -> (b,a+b))
        (fun (a,b)->a)