def f2(x):
    d, m = divmod(x, 10)
    return d + m


def f(x):
    while x >= 10:
        x = f2(x)
    return x


def fun_main(p):
    while len(p) > 1:
        p[-2] *= f(p[-1])
        p.pop()
    return f(p.pop())


_ = input()
print(fun_main([*map(int, input().split())]))