N = int(input())
T = {}
for i in range(1,N+1):
    T[i]=[]
for i in range(N):
    A,B = map(int,input().split())
    T[A].append(i+1)
    T[B].append(i+1)

talal = False
while not talal:
    keves = []
    for kulcs,ertek in T.items():
        if len(ertek) <= 1:
            keves.append(kulcs)
    if len(keves) == 0:
        talal = True
    else:
        for kulcs,ertek in T.items():
            marad = []
            for k in ertek:
                if k not in keves:
                    marad.append(k)
            T[kulcs] = marad
        for k in keves:
            T.pop(k)
print(len(T))
for k in T.keys():
    print(k,end=" ")