from sys import stdin
n, *indata = map(int, stdin.read().split())
offset = 0
g = [0 for i in range((10**5)*2+1)]
ginv = [0 for i in range((10**5)*2+1)]
for i in range(n):
    s, t = indata[offset + 2*i],indata[offset + 2*i+1]
    g[s] += 1
    ginv[t] += 1

plusused = False
minusused = False
for i in range(1,(10**5)*2+1):
    if abs(g[i] - ginv[i]) >= 2:
        print("{}".format(0))
        exit()
    elif g[i] - ginv[i] == 1:
        if plusused:
            print("{}".format(0))
            exit()
        else:
            plusused = True
    elif g[i] - ginv[i] == 1:
        if minusused:
            print("{}".format(0))
            exit()
        else:
            minusused = True

if plusused:
    print("{}".format(1))
    exit()

ans = 0
for i in range(1,(10**5)*2+1):
    if g[i]:
        ans += 1
print("{}".format(ans))