mas=[]
for i in range(1000):
a=int(input())
if a==0: break
if a>9 and a<100:
mas.append(a)
if sum(mas)!=0:
print(sum(mas)/len(mas))
else:
print('NO')
школа 1747
mas=[]
for i in range(1000):
a=int(input())
if a==0: break
if a>9 and a<100:
mas.append(a)
if sum(mas)!=0:
print(sum(mas)/len(mas))
else:
print('NO')