Digital Root

Add up the digits of n. If the result has more than one digit, add up its digits again. Repeat until a single digit remains.

Implement digital_root(n).

Input

n: A positive integer.

Output

Return the final single digit.

Vincoli

1 ≤ n ≤ 10¹⁸

Esempi

Input:
n = 999

Output atteso:
expected = 9

Input:
long long n = 999;

Output atteso:
long long expected = 9;

Input:
long n = 999;

Output atteso:
long expected = 9;

Input:
n = 38

Output atteso:
expected = 2

Input:
long long n = 38;

Output atteso:
long long expected = 2;

Input:
long n = 38;

Output atteso:
long expected = 2;