n = int(input())
ge = 0
z = 0
for i in range(n):
    l = list(map(int, input().split()))
    s = ge
    if s != 0:
        for j in range(s):
            t = l[j]
            if t != 0:
                z = z + 1
    ge = ge + 1
if z == 0:
    print('YES')
else:
    print('NO')