5124: Bear and Drawing
内存限制：256 MB
时间限制：2 S
题面：传统
评测方式：文本比较
上传者：
提交：1
通过：1
题目描述
C. Bear and Drawing
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
Limak is a little bear who learns to draw. People usually start with houses, fences and flowers but why would bears do it? Limak lives in the forest and he decides to draw a tree.
Recall that tree is a connected graph consisting of n vertices and n-1 edges.
Limak chose a tree with n vertices. He has infinite strip of paper with two parallel rows of dots. Little bear wants to assign vertices of a tree to some n distinct dots on a paper so that edges would intersect only at their endpoints − drawn tree must be planar. Below you can see one of correct drawings for the first sample test.
Is it possible for Limak to draw chosen tree?
Recall that tree is a connected graph consisting of n vertices and n-1 edges.
Limak chose a tree with n vertices. He has infinite strip of paper with two parallel rows of dots. Little bear wants to assign vertices of a tree to some n distinct dots on a paper so that edges would intersect only at their endpoints − drawn tree must be planar. Below you can see one of correct drawings for the first sample test.
Is it possible for Limak to draw chosen tree?
Input
The first line contains single integer n (1≤n≤105). Next n-1 lines contain desc
Output
Print "Yes" (without the quotes) if Limak can draw chosen tree. Otherwise, print "No" (without the quotes).
Examples
Input
8 1 2 1 3 1 6 6 4 6 7 6 5 7 8
Output
Yes
Input
13 1 2 1 3 1 4 2 5 2 6 2 7 3 8 3 9 3 10 4 11 4 12 4 13
Output
No
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输出样例 复制