// Arup Guha
// 3/22/2022
// Solution to 2014 SWERC Problem Book Club to illustrate network flow.
// Kattis link: https://open.kattis.com/problems/bookclub

import java.util.*;

public class bookclub {

	public static void main(String[] args) {
	
		Scanner stdin = new Scanner(System.in);
		int numP = stdin.nextInt();
		int numE = stdin.nextInt();
		Dinic mine = new Dinic(2*numP);
		
		// Add edges from source to people giving books.
		for (int i=0; i<numP; i++)
			mine.add(2*numP, i, 1, 0);
			
		// Add edges from people receiving books to sink.
		for (int i=numP; i<2*numP; i++)
			mine.add(i, 2*numP+1, 1, 0);
		
		// Go through the edges.
		for (int i=0; i<numE; i++) {
			
			// We want our edge to go from the second person to the first.
			// Added numP to first item because this is the vertex number in my network flow graph.
			int v = stdin.nextInt() + numP;
			int u = stdin.nextInt();
			
			// Add this edge.
			mine.add(u, v, 1, 0);
		}
		
		// Get the max flow.
		int res = mine.flow();
		
		// Output accordingly.
		if (res == numP)
			System.out.println("YES");
		else
			System.out.println("NO");
	
	}
}

// An edge connects v1 to v2 with a capacity of cap, flow of flow.
class Edge {
	int v1, v2, cap, flow;
	Edge rev;
	Edge(int V1, int V2, int Cap, int Flow) {
		v1 = V1;
		v2 = V2;
		cap = Cap;
		flow = Flow;
	}
}

class Dinic {

	// Queue for the top level BFS.
	public ArrayDeque<Integer> q;

	// Stores the graph.
	public ArrayList<Edge>[] adj;
	public int n;

	// s = source, t = sink
	public int s;
	public int t;


	// For BFS.
	public boolean[] blocked;
	public int[] dist;

	final public static int oo = (int)1E9;

	// Constructor.
	public Dinic (int N) {

		// s is the source, t is the sink, add these as last two nodes.
		n = N; s = n++; t = n++;

		// Everything else is empty.
		blocked = new boolean[n];
		dist = new int[n];
		q = new ArrayDeque<Integer>();
		adj = new ArrayList[n];
		for(int i = 0; i < n; ++i)
			adj[i] = new ArrayList<Edge>();
	}

	// Just adds an edge and ALSO adds it going backwards.
	public void add(int v1, int v2, int cap, int flow) {
		Edge e = new Edge(v1, v2, cap, flow);
		Edge rev = new Edge(v2, v1, 0, 0);
		adj[v1].add(rev.rev = e);
		adj[v2].add(e.rev = rev);
	}

	// Runs other level BFS.
	public boolean bfs() {

		// Set up BFS
		q.clear();
		Arrays.fill(dist, -1);
		dist[t] = 0;
		q.add(t);

		// Go backwards from sink looking for source.
		// We just care to mark distances left to the sink.
		while(!q.isEmpty()) {
			int node = q.poll();
			if(node == s)
				return true;
			for(Edge e : adj[node]) {
				if(e.rev.cap > e.rev.flow && dist[e.v2] == -1) {
					dist[e.v2] = dist[node] + 1;
					q.add(e.v2);
				}
			}
		}

		// Augmenting paths exist iff we made it back to the source.
		return dist[s] != -1;
	}

	// Runs inner DFS in Dinic's, from node pos with a flow of min.
	public int dfs(int pos, int min) {

		// Made it to the sink, we're good, return this as our max flow for the augmenting path.
		if(pos == t)
			return min;
		int flow = 0;

		// Try each edge from here.
		for(Edge e : adj[pos]) {
			int cur = 0;

			// If our destination isn't blocked and it's 1 closer to the sink and there's flow, we
			// can go this way.
			if(!blocked[e.v2] && dist[e.v2] == dist[pos]-1 && e.cap - e.flow > 0) {

				// Recursively run dfs from here - limiting flow based on current and what's left on this edge.
				cur = dfs(e.v2, Math.min(min-flow, e.cap - e.flow));

				// Add the flow through this edge and subtract it from the reverse flow.
				e.flow += cur;
				e.rev.flow = -e.flow;

				// Add to the total flow.
				flow += cur;
			}

			// No more can go through, we're good.
			if(flow == min)
				return flow;
		}

		// mark if this node is now blocked.
		blocked[pos] = flow != min;

		// This is the flow
		return flow;
	}

	public int flow() {
		clear();
		int ret = 0;

		// Run a top level BFS.
		while(bfs()) {

			// Reset this.
			Arrays.fill(blocked, false);

			// Run multiple DFS's until there is no flow left to push through.
			ret += dfs(s, oo);
		}
		return ret;
	}

	// Just resets flow through all edges to be 0.
	public void clear() {
		for(ArrayList<Edge> edges : adj)
			for(Edge e : edges)
				e.flow = 0;
	}
}