https://www.nowcoder.com/practice/5427af99168b45f4a14aec195b28a839?tpId=98&&tqId=32999&rp=1&ru=/acti

#include
#include
#include
#define maxn 100020
#define maxm 200020
using namespace std;
int tot = 0, n;
int fir[maxn], en[maxm], nex[maxm]; 

int f[maxn][2];
int fa[maxn];

void add_edge(int x, int y){
    en[++tot] = y;
    nex[tot] = fir[x];
    fir[x] = tot;
}
void dfs(int x){
    for( int k = fir[x] ; k ; k = nex[k] ){
        int j = en[k];
        if( j == fa[x])continue;
        fa[j] = x;
        dfs(j);
        f[x][0] += f[j][0] + 2;
    }
    f[x][1] = f[x][0];
    for( int k = fir[x]; k ; k = nex[k]){
        int j = en[k];
        if( j == fa[x])continue;
        f[x][1] = min(f[x][1], f[x][0] - f[j][0] + f[j][1] - 1);
    }
}
int main(){
    scanf("%d", &n);
    for( int i = 1; i <= n - 1 ; i ++ ){
        int x, y;
        scanf("%d%d", &x, &y);
        add_edge(x, y);
        add_edge(y, x);
    }
    dfs(1);
    printf("%d\n", f[1][1]);
    return 0;
}