UVA1218PerfectService

//UVA1218PerfectService
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
const int MAXN = 1e4 + 10;
const int INF = 1e9;
vector<int> G[MAXN], vertices;
int d[MAXN][3], p[MAXN]; 
void dfs(int now, int father) {
	p[now] = father;
	vertices.push_back(now);
	for(int i = 0; i < G[now].size(); i++) {
		int v = G[now][i];
		if(father == v) continue;
		dfs(v, now);
	} 
}//定好dp遍历时的顺序 


int main() {
	int N;
	while(scanf("%d", &N) == 1 && N != -1) {
		int a, b;
		vertices.clear();
		for(int i = 0; i <= N; i++) G[i].clear();
	    for(int i = 0; i < N - 1; i++) {
	    	scanf("%d%d", &a, &b); 
	    	a--; b--;
	    	G[a].push_back(b);
	    	G[b].push_back(a);
		}//建图 
		
		dfs(0, -1);//建立之后动态规划的遍历顺序 
	
	    for(int k = vertices.size() - 1; k >= 0; k--) {
	    	int u = vertices[k];
	    	//
			d[u][0] = 1; d[u][1] = 0;
	    	//若k是服务器，则将d[k]初始化为1，否则初始化为0 
	    	
			for(int i = 0; i < G[u].size(); i++) {
			    //printf("u = %d\n", vertices[k]);
	    		int v = G[u][i];
				if(v == p[u]) continue; //遇到父节点则跳过
				d[u][0] += min(d[v][0], d[v][1]);
				//printf("d[u][0] = %d, d[u][1] = %d\n", d[u][0], d[u][1]);
				d[u][1] += d[v][2];
			    if(d[u][0] > INF) d[u][0] = INF;
			    if(d[u][1] > INF) d[u][1] = INF;
			} 
			d[u][2] = INF;
			for(int i = 0; i < G[u].size(); i++) {
				int v = G[u][i];
				if(v == p[u]) continue;
				d[u][2] = min(d[u][1] - d[v][2] + d[v][0], d[u][2]);
				//printf("d[u][2] = %d\n", d[u][2]);
			}
		}
	    printf("%d\n", min(d[0][0], d[0][2]));
		int flag;
		scanf("%d", &flag);
		if(flag == -1) break;
	}
	return 0;
}
/*
6
1 3
2 3
3 4
4 5
4 6
0
2
1 2
-1
*/