N = int(input())

C = 2 * (10 ** 5 ) + 1
hidari = [0] * C
migi = [0] * C
gyouretu = []
for _ in range(N):
    h,w = map(int,input().split())
    gyouretu.append((h,w))
    hidari[h] += 1
    migi[w] += 1
import sys
hidaricount = 0
migicount = 0
for i in range(1,C):
    if hidari[i] > migi[i]:
        hidaricount += hidari[i] - migi[i]
        ih = i
    elif hidari[i] < migi[i]:
        migicount += migi[i] - hidari[i]
        im = i
if hidaricount > 1 or migicount > 1:
    print(0)
    exit()
if hidaricount == 1:
    for h,w in gyouretu:
        if h == ih and w == im:
            print(0)
            exit()
    print(1)
    exit()
ans = 0
for i in hidari:
    if i != 0:
        ans += 1
print(ans)