#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
#include<algorithm>
#include<string>
#include<math.h>
#pragma comment(linker, "/STACK:66777216")

using namespace std;

#define ll unsigned _int64
ll n, m;
vector<ll>u;
vector<vector<ll>>g;

void dfs(ll v) {
    u[v] = 1;
    for (ll to : g[v]) {
        if (u[to] == 1) {
            cout << "NO";
            exit(0);
        }
        else if (!u[to]) dfs(to);
    }
    u[v] = 2;
}

int main(void) {
    ios_base::sync_with_stdio(false);
    //  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    //  #endif

    cin >> n >> m;
    g.resize(n);
    u.resize(n);
    string s = "YES";
    if (n - m != 1) s = "NO";
    if (n == 1) {
        cout << s;
        exit(0);
    }
    for (ll i = 0; i < m; i++) {
        ll a, b;
        cin >> a >> b;
        g[a - 1].push_back(b - 1);
        g[b - 1].push_back(a - 1);
    }
    dfs(g[0][0]);
    for (ll a : u) {
        if (!a) {
            cout << "NO";
            exit(0);
        }
    }
    cout << s;

}