#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;

const int MAXN = 1005;
vector<int> g[MAXN];
int num[MAXN];
int h;

void MakeTree(int u, int fat, int x)
{
    h = max(h, x);
    num[x]++;
    for (int i = 0; i < g[u].size(); i++)
    {
        int v = g[u][i];
        if (v != fat) MakeTree(v, u, x + 1);
    }
}

int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        for (int i = 1; i <= n; i++)
            g[i].clear();
        h = 0;
        memset(num, 0, sizeof(num));
        for (int i = 1; i < n; i++)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            g[u].push_back(v);
            g[v].push_back(u);
        }
        MakeTree(1, 0, 1);
        bool flag = true;
        for (int i = 1; i < h; i++)
        {
            if (num[i] > 1)
            {
                flag = false;
                break;
            }
        }
        if (flag) printf("YES\n");
        else printf("NO\n");
    }
    return 0;
}