#define _CRT_SECURE_NO_WARNINGS
#include "stdafx.h"
#include "stdio.h"
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <set>


using namespace std;
void dfs(int &v, vector<vector<int>> &a, vector<bool> &used, int &cnt)
{
	used[v] = true;
	cnt++;
	for (int i = 0; i < a[v].size(); ++i)
		if (!used[a[v][i]])
			dfs(a[v][i], a, used, cnt);
}
void main()
{
#ifdef _DEBUG
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
	int n, m, cnt, flag = 1;
	cin >> n >> m;
	vector<vector<int>> a (n);
	vector<bool> used(n);
	for (int i = 0; i < m; ++i)
	{
		int ch, ch1;
		ch--, ch1--;
		a[ch].push_back(ch1);
		a[ch1].push_back(ch);
	}
	for (int i = 0; i < n; ++i)
		if (!used[i])
		{
			dfs(i, a, used, cnt = -1);
			if (a[i].size() == cnt)
				flag *= 1;
			else
				flag *= 0;
		}
	if (flag == 1)
		cout << "YES";
	else
		cout << "NO";
}