n = int(input())

par = [i for i in range(200000)]
sz = [1] * 200000

def find(k):
    if par[k] == k:
        return k
    par[k] = find(par[k])
    return par[k]

def merge(k, l):
    k = find(k)
    l = find(l)
    if k == l:
        return
    if sz[k] > sz[l]:
        k, l = l, k
    par[k] = l
    sz[l] += sz[k]

count_h = [0] * 200000
count_w = [0] * 200000
for i in range(n):
    h, w = map(int, input().split())
    h -= 1
    w -= 1
    count_h[h] += 1
    count_w[w] += 1
    merge(h, w)

root = -1
for i in range(200000):
    if count_h[i] + count_w[i]:
        if root == -1:
            root = find(i)
        elif find(i) != root:
            print(0)
            exit()

ans = 0
diff = []
for i in range(200000):
    if abs(count_h[i] - count_w[i]) > 1:
        print(0)
        exit()
    elif count_h[i] != count_w[i]:
        diff.append(i)
    elif count_h[i]:
        ans += 1
if len(diff) > 2:
    print(0)
elif diff:
    print(1)
else:
    print(ans)