n = int(input())
count_h = [0] * 200000
count_w = [0] * 200000
loop = [0] * 200000
for i in range(n):
    h, w = map(int, input().split())
    h -= 1
    w -= 1
    if h == w:
        loop[h] += 1
    else:
        count_h[h] += 1
        count_w[w] += 1
ans = 0
diff = []
for i in range(200000):
    if abs(count_h[i] - count_w[i]) > 1:
        print(0)
        exit()
    elif count_h[i] == 0 and count_w[i] == 0 and loop[i] != 0 and loop[i] != n:
        print(0)
        exit()
    elif count_h[i] != count_w[i]:
        diff.append(i)
    elif count_h[i] or loop[i]:
        ans += 1
if len(diff) > 2:
    print(0)
    exit()
if diff:
    print(1)
else:
    print(ans)