MOD = 10 ** 9 + 7
INF = 10 ** 10
import sys
input = sys.stdin.readline
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)

def digitsum(n):
    ans = 0
    power = 10
    for _ in range(int(n//10) + 1):
        ans += n%power
        n //= power
        power *= 10
    return ans

def main():
    n = int(input())
    p = [digitsum(int(i)) for i in input().split()]

    ans = 1
    for pi in p:
        ans *= pi
    
    while ans//10 > 0:
        ans = digitsum(ans)
    print(ans)
if __name__ =='__main__':
    main()