F fib_iter(n)
   I n < 2
      R n
   V fib_prev = 1
   V fib = 1
   L 2 .< n
      (fib_prev, fib) = (fib, fib + fib_prev)
   R fib

L(i) 1..20
   print(fib_iter(i), end' ‘ ’)
print()