n = int(input())
N = 2*10**5+1
ind = [0]*N
out = [0]*N
for _ in range(n):
    h,w = map(int,input().split())
    ind[h] += 1
    out[w] += 1
nonzero = [i for i in range(N) if ind[i] != out[i]]
if len(nonzero) == 0:
    ans = sum(ind[i]+out[i] > 0 for i in range(N))
elif len(nonzero) == 2:
    i,j = nonzero
    if abs(ind[i] - out[i]) == 1:
        ans = 1
    else:
        ans = 0
else:
    ans = 0
print(ans)