...

#include<stdio.h>

int main (){
    int n ;
    scanf("%d",&n);
    int count[1000]={0};
    for (int i=1;i<=n-1;i++){
        int a, b;
        scanf("%d",&a);
        scanf("%d",&b);
        count[a]++;
        count[b]++;
    }
    int flag = 0 ;
    for (int i=1;i<=n-1;i++){
        if (count[i]==n-1){
            flag=1;
            break;
        }
    }
    if ( flag ){
        printf("YES");
    }
    else printf("NO");
    return 0;
}