from scipy.sparse.csgraph import connected_components
from scipy.sparse import csr_matrix

from collections import Counter

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

matr = csr_matrix(([1] * N, (frm, to)), shape=(MAX, MAX))
_, labels = connected_components(matr)

# 連結か
if len(set(labels[x] for x in st)) == 1:
    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)
else:
    print(0)