#include <bits/stdc++.h>

#define sz(a) (int)a.size()
#define re return
#define fi first
#define se second
#define pb push_back
#define all(a) a.begin(), a.end()

#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
#pragma GCC optimize("fast-math")

using namespace std;

typedef long long ll;
typedef string str;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<ll> vll;
typedef vector<int>vi;

int n, m, st;
bool ma[101][101], used[101];
void dfs (int v, int pr) {
   for(int i = 0; i < n; ++i)
      if(i != pr && used[i] && ma[i][v])
      {
         cout << "NO";
         exit(0);
      }
      else
         if(i != pr && ma[i][v])
         {
            dfs(i, v);
            used[v] = 1;
         }
   used[v] = 1;
}


///!!!<3<3<3<3<3!!!
void ProdamGaraje ()
{
   cin >> n >> m;
   for (int i = 0; i < m; ++i) {
      int x, y;
      cin >> x >> y;
      x--; y--;
      if(ma[x][y] || x == y)
      {
         cout << "NO";
         re;
      }
      ma[x][y] = 1;
      ma[y][x] = 1;
      st = x;
   }
   used[st] = 1;
   dfs(st, st);
   cout << "YES";
}
///!!!<3<3<3<3<3!!!
int main ()
{
   freopen ("tree.in", "r", stdin);
   freopen ("tree.out", "w", stdout);
   ios::sync_with_stdio(0);
   cin.tie(0); cout.tie(0);
   int tt = 1;
   //cin >> tt;
   while (tt--)
      ProdamGaraje ();
}
///GOOOOOOSE!!!!
/*
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