n=int(input())
xs=list(map(int,input().split(" ")))
r=1
for x in xs:
	r*=x
while len(str(r))>1:
	r2=str(r)
	r3=0
	for i in range(0,len(r2)):
		r3+=int(r2[i])
	r=r3
print(r)