#include <bits/stdc++.h>
using namespace std;
const int INF = (int)1e9;
const int EPS = 1e-8;
const int MOD = 1000000007;
const long double PI = 3.14159265359;
inline bool inside(int x, int y, int n, int m) {
  return x >= 1 && x <= n && y >= 1 && y <= m;
}
template <typename T>
T gcd(T a, T b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
template <typename ForwardIterator, typename T>
T first_val(ForwardIterator first, ForwardIterator last, T value) {
  auto it = std::lower_bound(first, last, value);
  return (it != last) ? (it - first) : -1;
}
template <typename ForwardIterator, typename T>
T last_val(ForwardIterator first, ForwardIterator last, T value) {
  auto it = std::upper_bound(first, last, value);
  return ((it != last) ? ((it - first) - 1) : -1);
}
template <typename T>
T Dis(T x1, T y1, T x2, T y2) {
  return sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2)));
}
template <typename T>
T Angle(T x1, T y1, T x2, T y2) {
  return atan((double)(y1 - y2) / (double)(x1 - x2));
}
int Set(int N, int pos) { return N = N | (1 << pos); }
int Reset(int N, int pos) { return N = N & ~(1 << pos); }
bool Check(int N, int pos) { return (bool)(N & (1 << pos)); }
template <class T, class X>
inline T togglebit(T a, X i) {
  T t = 1;
  return (a ^ (t << i));
}
long long int lcm(long long int a, long long int b) {
  return (long long int)((long long int)(a * b) / gcd(a, b));
}
bool compare(const pair<long long int, long long int> &i,
             const pair<long long int, long long int> &j) {
  return i.second > j.second;
}
int doubleCompare(double x, double y) {
  if (fabs(x - y) <= EPS) return 0;
  if (x < y) return -1;
  return 1;
}
int countSetBits(int n) {
  int count = 0;
  while (n > 0) {
    count += (n & 1);
    n = n >> 1;
  }
  return count;
}
int getPosBit(long long int n, int k) { return (n & (1 << k)) != 0 ? 1 : 0; }
void setPosBit(int &n, int k) { n = n | (1 << k); }
long long int fast_power(int a, int x) {
  if (x == 0)
    return 1;
  else if (x == 1)
    return a;
  else {
    long long int R = fast_power(a, x >> 1);
    if (!(x & 1))
      return R * R;
    else
      return R * a * R;
  }
}
long long int fast_power_unlocked(long long int a, long long int n,
                                  long long int mod) {
  long long int res = 1;
  while (n > 0) {
    if (n & 1) {
      res = (res * a) % mod;
    }
    a = (a * a) % mod;
    n = n >> 1;
  }
  return res;
}
long long int modInverse(long long int A, long long int M) {
  return fast_power_unlocked(A, M - 2, M);
}
const int MAX_N = 2 * 1e3;
vector<int> par;
vector<int> node;
vector<int> edge;
int find(int x) {
  if (par[x] == x) return par[x];
  return par[x] = find(par[x]);
}
void Union(int a, int b) {
  int x = find(a);
  int y = find(b);
  if (x == y) {
    edge[x]++;
    return;
  }
  if (node[x] < node[y]) {
    swap(x, y);
  }
  par[y] = x;
  node[x] += node[y];
  edge[x] += edge[y];
  edge[x]++;
}
void solve() {
  int n, m;
  cin >> n >> m;
  par.resize(n);
  node.resize(n);
  edge.assign(n, 0);
  for (int i = 0; i < n; i++) {
    par[i] = i, node[i] = 1;
  }
  int s, e;
  for (int i = 0; i < m; i++) {
    cin >> s >> e;
    s--;
    e--;
    Union(s, e);
  }
  for (int i = 0; i < n; i++) {
    if ((node[find(i)] * 1LL * (node[find(i)] - 1)) / 2 !=
        edge[find(i)] * 1LL) {
      cout << "NO";
      return;
    }
  }
  cout << "YES";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ;
  for (auto blockTime = make_pair(chrono::high_resolution_clock::now(), true);
       blockTime.second;
       fprintf(stderr, "%s: %lld ms\n", "Time Taken",
               chrono::duration_cast<chrono::milliseconds>(
                   chrono::high_resolution_clock::now() - blockTime.first)
                   .count()),
            fflush(stderr), blockTime.second = false) {
    solve();
  }
}
