from collections import Counter

N = int(input())
MAX = 2 * 10 ** 5
deg = [0] * MAX
st = set()
for _ in range(N):
    H, W = (int(x) - 1 for x in input().split())
    deg[H] += 1
    deg[W] -= 1
    st.add(H)
    st.add(W)

ct = Counter(deg)
if ct[0] == MAX:
    print(len(st))
elif ct[0] == MAX - 2 and ct[-1] == ct[1] == 1:
    print(1)
else:
    print(0)