n=int(input())
a=[list(map(int, input().split())) for i in range(n)]

M=200001
X=[0]*M
Y=[0]*M
for x, y in a:
    X[x]+=1
    Y[y]+=1
c=0
for i in range(M):
    c+=abs(X[i]-Y[i])
if c==0:
    ans=0
    for i in range(M):
        if X[i]>0 or Y[i]>0:
            ans+=1
    print(ans)
elif c==1:
    print(1)
else:
    print(0)