public void testing() throws IOException{

throw new IOException("");

}

static ArrayList<ArrayList<Integer>> a;

static int vis[];

static boolean cycle = false, moreCom = false;

public static void dfs(int i) {

for(int j=0;j<a.get(i).size();j++) {

int vertex = a.get(i).get(j);

if(vis[vertex] != 0 && vis[i] != vertex && vis[i] != i) {

//System.out.println("we reached here");

cycle = true;

return;

}

else if(vis[vertex] == 0) {

vis[vertex] = i;

dfs(vertex);

}

}

}

public static void main(String args[]) throws java.io.IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

String s[] = br.readLine().split(" ");

int n = Integer.parseInt(s[0]);

int e = Integer.parseInt(s[1]);

a = new ArrayList<>();

for(int i=0;i<n+1;i++) a.add(new ArrayList<>());

vis = new int[n+1];

for(int i=0;i<e;i++) {

String s1[] = br.readLine().split(" ");

int st = Integer.parseInt(s1[0]);

int en = Integer.parseInt(s1[1]);

a.get(st).add(en);

a.get(en).add(st);

}

int cnt = 0;

for (int i=1;i<=n;i++) {

if(cnt == 0 && vis[i] == 0) {

vis[i] = i;

cnt++;

dfs(i);

}

else if(cnt >= 1 && vis[i] == 0) {

//System.out.println("we reached here 2");

moreCom = true;

break;

}

}

//for(ArrayList<Integer> aa: a) System.out.println(aa);

//System.out.println(Arrays.toString(vis));

//if(e == 0) System.out.println("NO");

if(!moreCom && !cycle) System.out.println("YES");

else System.out.println("NO");

}