Function f with natural arguments and values is defined like this:
f(0) = 0
f(1) = 1
f(2n) = f(n)
f(2n + 1) = f(n) + f(n + 1)
Compose a program to calculate f(n) given n.
Input
Given a single number n (1 ≤ n ≤ 1018).
Output
for;while;until