import numpy as np


def solve():
    N = int(input())
    P = np.array(input().split(), dtype='int64')

    K = list(str(np.prod(P)))
    while len(K) != 1:
        num = 0
        for k in K:
            num += int(k)
        K = list(str(num))
    print(K[0])


if __name__ == '__main__':
    solve()