def main():
    N = int(input())
    P = list(map(int, input().split()))
    A = 1
    for p in P:
        A *= p

    ans = str(A)
    while len(ans) > 1:
        tmp = 0
        for a in ans:
            tmp += int(a)
        ans = str(tmp)

    print(ans)

if __name__ == "__main__":
    main()