#!/usr/bin/env python3
import sys, math, itertools, heapq, collections, bisect
input = lambda: sys.stdin.buffer.readline().rstrip().decode('utf-8')
sys.setrecursionlimit(10**8)
inf = float('inf')
ans =tmp=0
count = 1

n=int(input())
if n==0:
    print(0)
    exit()
P=list(map(int,input().split()))
for i in range(n):
    count*=P[i]
count=list(map(int,list(str(count))))
while len(count)!=1:
    count = list(map(int, list(str(sum(count)))))
print(count[0])
# print(ans)