空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld
题目描述
You are given an undirected tree consisting of $$$n$$$ vertices. An undirected tree is a connected undirected graph with $$$n - 1$$$ edges.
Your task is to add the minimum number of edges in such a way that the length of the shortest path from the vertex $$$1$$$ to any other vertex is at most $$$2$$$. Note that you are not allowed to add loops and multiple edges.
输入描述:
The first line contains one integer $$$n$$$ ($$$2 \le n \le 2 \cdot 10^5$$$) — the number of vertices in the tree.
The following $$$n - 1$$$ lines contain edges: edge $$$i$$$ is given as a pair of vertices $$$u_i, v_i$$$ ($$$1 \le u_i, v_i \le n$$$). It is guaranteed that the given edges form a tree. It is guaranteed that there are no loops and multiple edges in the given edges.
输出描述:
Print a single integer — the minimum number of edges you have to add in order to make the shortest distance from the vertex $$$1$$$ to any other vertex at most $$$2$$$. Note that you are not allowed to add loops and multiple edges.
备注:
The tree corresponding to the first example:
The answer is $$$2$$$, some of the possible answers are the following: $$$[(1, 5), (1, 6)]$$$, $$$[(1, 4), (1, 7)]$$$, $$$[(1, 6), (1, 7)]$$$.
The tree corresponding to the second example:
The answer is $$$0$$$.
The tree corresponding to the third example:
The answer is $$$1$$$, only one possible way to reach it is to add the edge $$$(1, 3)$$$.