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