sub fibonacciI (n)
    local n1, n2, k, sum

    n1 = 0
    n2 = 1
    for k = 1 to abs(n)
        sum = n1 + n2
        n1 = n2
        n2 = sum
    next k
    if n < 1 then
       return n1 * ((-1) ^ ((-n) + 1))
    else
       return n1
    end if
end sub