class Unionfind:
     
    def __init__(self,n):
        self.uf = [-1]*n
 
    def find(self,x):
        if self.uf[x] < 0:
            return x
        else:
            self.uf[x] = self.find(self.uf[x])
            return self.uf[x]
 
    def same(self,x,y):
        return self.find(x) == self.find(y)
 
    def union(self,x,y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return False
        if self.uf[x] > self.uf[y]:
            x,y = y,x
        self.uf[x] += self.uf[y]
        self.uf[y] = x
        return True
 
    def size(self,x):
        x = self.find(x)
        return -self.uf[x]
n = int(input())
M = 2*10**5+5
count = [0]*M
use = [0]*M
uf = Unionfind(M)
for i in range(n):
    h,w = map(int,input().split())
    count[h] += 1
    count[w] -= 1
    use[h] = 1
    use[w] = 1
    uf.union(h,w)
p = 0
m = 0
for i in range(M):
    if use[i]:
        if uf.size(i) != sum(use):
            print(0)
            exit()
        else:
            break
for i in range(M):
    if use[i]:
        if count[i] == 0:
            continue
        if abs(count[i]) != 1:
            print(0)
            exit()
        if count[i] == 1:
            p += 1
        else:
            m += 1
if p == m == 0:
    print(sum(use))
elif p == m == 1:
    print(1)
else:
    print(0)