#include<bits/stdc++.h>
using namespace std;
int n;
bool kt=1;
vector<int> e[1010];
void utd(int u)
{
int cnt=0;
for (int i=0;i<e[u].size();i++)
{
int v=e[u][i];
utd(v);
cnt++;
if (cnt>2) { kt=0; return; }
}
if (cnt==1) { kt=0; return; }
}
int main()
{
cin>>n;
int u,v;
for (int i=1;i<n;i++)
{
cin>>u>>v;
e[u].push_back(v);
if (e[u].size()>2) { cout<<"no"; return 0; }
}
utd(0);
if (kt) cout<<"yes";
else cout<<"no";
return 0;
}
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