N=int(input())
P=list(map(int,input().split()))

A=P[0]
while len(str(A))>1:
    Q=0
    for q in str(A):
        Q+=int(q)
    A=Q

for p in P[1:]:
    B=0
    for q in str(p):
        B+=A*int(q)

    A=B

    while len(str(A))>1:
        Q=0
        for q in str(A):
            Q+=int(q)
        A=Q
print(A)