#include <bits/stdc++.h>

#define close_all { \
out.close();      \
in.close(); }

using namespace std;

#define int long long

int n;
map<int, vector<int>> graph;
map<int, bool> used;
set<int> curr;
map<int, bool> root;
bool chk;

void dfs(int v) {
  used[v] = true;
  curr.insert(v);
  for (auto dest : graph[v]) {
    if (!used[dest]) {
      dfs(dest);
    }
  }
}

signed main() {
  int m;
  cin >> n >> m;

  if (m != n - 1) {
    chk = true;
  }

  set<int> c;

  for (int i = 0; i < m; ++i) {
    int a, b;
    cin >> a >> b;
    graph[a - 1].push_back(b - 1);
    graph[b - 1].push_back(a - 1);
  }

  dfs(0);
  if (curr.size() != n) {
    chk = true;
  }

  if (chk) {
    cout << "no";
  } else {
    cout << "yes";
  }
  return 0;
}