n = int(input())
max_ = 2 * 10 ** 5
edges = [[] for _ in range(max_)]
in_cnt = [0] * max_
out_cnt = [0] * max_
for _ in range(n):
    h, w = map(int, input().split())
    h -= 1
    w -= 1
    edges[h].append(w)
    in_cnt[h] += 1
    out_cnt[w] += 1
    
s = -1
g = -1

for j, (i, o) in enumerate(zip(in_cnt, out_cnt)):
    if i == o:
        continue
    if i == o + 1:
        if s == -1:
            s = j
        else:
            print(0)
            exit()
    elif i + 1 == o:
        if g == -1:
            g = j
        else:
            print(0)
            exit()
    else:
        print(0)
        exit()
        
if s == g == -1:
    ans = 0
    for e in edges:
        ans += len(set(e))
    print(ans)
    exit()

cnt = 0
used = [False] * n
stack = [s]
used[s] = True
while stack:
    pos = stack.pop()
    for npos in edges[pos]:
        if used[npos]:
            continue
        if npos == g:
            cnt += 1
            continue
        used[npos] = True
        stack.append(npos)

l = 0
for e in edges:
    if g in e: l += 1

if cnt == 1:
    print(max(1, l - 1))
else:
    print(l)