import numpy as np


def solve():
    N, *P = map(int, open(0).read().split())

    K = 1
    for p in P:
        K *= p
    K = str(K)
    while len(K) != 1:
        num = 0
        for k in K:
            num += int(k)
        K = str(num)
    print(K)


if __name__ == '__main__':
    solve()