n = int(input())
a = []
s = 0
k = 0
for i in range(n):
    a.append(list(map(int, input().split())))
for i in range(n):
    for j in range(n):
        if i < j and a[i][j] % 2 != 0:
            s += a[i][j]
            k += 1
if k == 0:
    print("No")
else:
    print(s/k)