13.21

from random import randrange as rnd
a = []
for i in range(10):
	a.append(rnd(10))
print(a)


n = len(a)
s = 0
for i in range(n):
	if a[i] == 0 and i != 0 and i != n-1:
		s = (a[i-1]+a[i+1])//2
		print(s)