#include<bits/stdc++.h>
using namespace std;
#define nl "\n"
#define fi first
#define se second
#define pb push_back
#define ll long long
#define ull unsigned ll
#define RV  return void
#define inf 2000000000
#define sz(x) int(x.size())
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define Mini(x) *min_element(all(x))
#define Maxi(x) *max_element(all(x))
#define fixed(n) fixed << setprecision(n)
// #define ceil(w, m) (((w) / (m)) + ((w) % (m) ? 1 : 0))
#define cin(v) for (auto&i:v) cin >> i;
#define cout(v) for (auto&i:v) cout << i << " ";
#define clr(memo, x) memset(memo, x, sizeof memo)
#define updmin(a, b) a = min(a, b)
#define updmax(a, b) a = max(a, b)
#define vi vector < int >
#define vl vector < ll >
#define vc vector < char >
#define vs vector < string >
#define v2i vector < vector < int > >
#define v2l vector < vector < int > >
#define seti set < int >
#define setl set < ll >
#define mapii map < int , int >
#define mapll map < ll , ll >
#define mapli map < ll , int >
#define mapci map < char , int >
#define mapsi map < string , int >
#define pll pair < ll , ll >
#define pii pair < int , int >
#define range(l,r,x) for(int i=l ; i < r ; i+=x)
#define FastCode ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
vector < string > ternary= {"NO\n" , "YES\n"};

void  Zainab(){
            #ifndef ONLINE_JUDGE
              freopen("input.txt", "r", stdin);
              freopen("output.txt", "w", stdout);
            #endif
}


/*================================  Prblem solution  ================================ */

vector < vector < int > > adj  , adj2;
vector < bool > vis;

bool dfs(int node , int par ){
    vis[node]=1;

    bool ans =0;
    //  connect with 2 nodes only or it is leaf

    if(sz(adj[node]) == 2 ) ans =1;
    else if (node ==1 ) ans =1;
    else if(sz(adj[node]) == 1 and node!=1 and adj[node][0]==par ) ans =1;
    else {
        // ans=0;
        // cout << node << nl;
        return 0;
    }

    for(auto& child : adj[node]){
         if(!vis[child]) {
               ans &= dfs(child , node);
         }
    }

    return ans ;
}


bool dfs2(int node , int target ){
    vis[node]=1;

    int cnt=0;
    if(target == node){
        cnt++;
        return cnt == 1 ;
    }
    for(auto& child : adj2[node]){
        cnt += dfs2(child , target);
    }

    return cnt == 1 ;
}

void myCode(){

int n , m ;
cin >> n  >> m ;
adj.assign (n+5 , vector < int > ());
vis.assign(n +5, 0);
adj2.assign(n+5 , vector < int > ());
for(int i =1 ; i < n ; i++){
  int u,v;
  cin >> u  >> v;
  adj[u].pb(v);
  adj[v].pb(u);

    adj2[u].pb(v);
}

if( m != n-1 ) RV(cout << "NO");




bool ans = dfs(1,1);
if(!ans) RV(cout << "NO");



//  what about cyclic ?

// check if there exist more than unique path from root to any node

for(int i =2 ; i <= n ; i++){
    vis.assign(n +5, 0);
    ans &= dfs2( 1 , i );
}

cout << ( ans ? "YES" : "NO");




}


int main(){
                                   FastCode ;
                                    Zainab() ;

    int testCase=1;
          // cin >> testCase ;
      for(int i=1 ; i<= testCase ; i++)
        myCode();

    return 0;
}