#include <iostream>
#include <vector>
#include <queue>
#include <list>

using namespace std;

int main ( int argc , char * argv[] ) {

    int t = 1;

    while ( t-- ) {
        int n;
        cin >> n;

        list<int> node[n];
        int visited[n];

        int p;
        cin >> p;

        int edge = p;

        for ( int i = 0 ; i < n ; i++ ) {
            visited[i] = 0;

            /*cout << "Node : " << i << " -> ";
            for ( vector<int>::iterator itr = node[i].begin() ; itr != node[i].end() ; itr++ ) {
                cout << *itr << " ";
            }
            cout << endl;
            */

        }


        while ( p-- ) {
            int a , b;
            cin >> a >> b;

            node[a-1].push_back(b-1);
            node[b-1].push_back(a-1);
        }


        queue<int> q;
        int count = 0;
        for ( int i = 0 ; i < n ; i++ ) {

            if ( visited[i] == 1 )
                continue;

            visited[i] = 1;

            q.push(i);

            while ( !q.empty() ) {
                int t = q.front();
                q.pop();

                for ( list<int>::iterator itr = node[t].begin() ; itr != node[t].end() ; itr++ ) {
                    int child = *itr;

                    if ( visited[child] == 1 )
                        continue;

                    visited[child] = 1;
                    q.push(child);
                }

            }

            count ++;


        }

        if ( count == 1 && n == edge  + 1 ) {
            cout << "YES" << endl;
        }
        else {
            cout << "NO" << endl;
        }


    }

    return 0;

}