Submission #63049269

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n=int(input())
g=[[]for _ in range(n)]
for _ in range(n-1):
    a,b=map(lambda x:int(x)-1,input().split())
    g[a].append(b)
    g[b].append(a)
import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')
for i in range(n):
    g[i].sort(key=lambda x:len(g[x]),reverse=True)
start=-1
for i in range(n):
    if len(g[i])>=4:
        start=i;break
if start==-1:
    exit(print(start))
import sys
sys.setrecursionlimit(10**6)
def dfs(now,prev=-1):
    cnt=1
 
 
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n=int(input())
g=[[]for _ in range(n)]
for _ in range(n-1):
    a,b=map(lambda x:int(x)-1,input().split())
    g[a].append(b)
    g[b].append(a)
import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')

for i in range(n):
    g[i].sort(key=lambda x:len(g[x]),reverse=True)
start=-1
for i in range(n):
    if len(g[i])>=4:
        start=i;break
if start==-1:
    exit(print(start))
import sys
sys.setrecursionlimit(10**6)
def dfs(now,prev=-1):
    cnt=1
    for v in g[now]:
        if len(g[v])<4:break
        if v==prev:continue
        cnt+=dfs(v,now)
    return cnt
m=dfs(start)
print(m*3+2)

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