l=[]
r=[]
ansss=0
def find(now,ans):
   # print(now,ans)
    global ansss
    if l[now]!=0:
        find(l[now],ans+1)
    if r[now]!=0 :
        find(r[now],ans+1)
    ansss=max(ans,ansss)
n=int(input())
l.append(0)
r.append(0)
for i in range(0,n):
    Ai=input()
    yyq=[int(i) for i in Ai.split()]
    l.append(yyq[0])
    r.append(yyq[1])
find(1,1)
print(ansss)