You are given a [directed graph](https://en.wikipedia.org/wiki/Directed_graph) consisting of n vertices and m edges (each edge is directed, so it can be traversed in only one direction). You are allowed to remove at most one edge from it.

Can you make this graph [acyclic](https://en.wikipedia.org/wiki/Directed_acyclic_graph) by removing at most one edge from it? A directed graph is called acyclic iff it doesn't contain any cycle (a non-empty path that starts and ends in the same vertex).

Input

The first line contains two integers n and m (2 ≤ n ≤ 500, 1 ≤ m ≤ min(n(n - 1), 100000)) — the number of vertices and the number of edges, respectively.

Then m lines follow. Each line contains two integers u and v denoting a directed edge going from vertex u to vertex v (1 ≤ u, v ≤ n, u ≠ v). Each ordered pair (u, v) is listed at most once (there is at most one directed edge from u to v).

Output

If it is possible to make this graph acyclic by removing at most one edge, print YES. Otherwise, print NO.

Examples

Input

3 4
1 2
2 3
3 2
3 1


Output

YES


Input

5 6
1 2
2 3
3 2
3 1
2 1
4 5


Output

NO

Note

In the first example you can remove edge <image>, and the graph becomes acyclic.

In the second example you have to remove at least two edges (for example, <image> and <image>) in order to make the graph acyclic.
import java.util.*;
import java.io.*;
import static java.lang.Math.*;
public class Main {
    static final long MOD = 1_000_000_007 , INF = 1_000_000_000_000_000L;
    static final int INf = 1_000_000_000;
    static FastReader reader;
    static PrintWriter writer;
    public static void main(String[] args) {
        Thread t = new Thread(null, new O(), "Integer.MAX_VALUE", 100000000);
        t.start();
    }
    static class O implements Runnable {
        public void run() {
            try {
                magic();
            }
            catch (Exception e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
    }
    static class FastReader {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public FastReader() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public FastReader(String file_name) throws IOException {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException {
            byte[] buf = new byte[1000000];
            int cnt = 0, c;
            while ((c = read()) != -1) {
                if (c == '\n') break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ') c = read();
            boolean neg = (c == '-');
            if (neg) c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg) return -ret;
            return ret;
        }

        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ') c = read();
            boolean neg = (c == '-');
            if (neg) c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg) return -ret;
            return ret;
        }

        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ') c = read();
            boolean neg = (c == '-');
            if (neg) c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (c == '.') while ((c = read()) >= '0' && c <= '9') ret += (c - '0') / (div *= 10);
            if (neg) return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1) buffer[0] = -1;
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead) fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException {
            if (din == null) return;
            din.close();
        }
    }
    static int n,m, ignoredu = -1, ignoredv = -1;
    static ArrayList<Integer> adj[];
    static ArrayList<Pair> edgesInCycle = new ArrayList<>();
    static boolean vis[], inStack[];
    static void magic() throws IOException {
        reader = new FastReader();
        writer = new PrintWriter(System.out, true);
        n = reader.nextInt();
        m = reader.nextInt();
        adj = new ArrayList[n+1];
        for(int i=1;i<=n;++i) {
            adj[i] = new ArrayList<>();
        }
        for(int i=0;i<m;++i) {
            int u = reader.nextInt(), v = reader.nextInt();
            adj[u].add(v);
        }
        vis = new boolean[n+1];
        inStack = new boolean[n+1];
        for(int i=1; i<=n; ++i) {
            if(!vis[i]) {
                dfs1(i, new Stack<>());
                if(!edgesInCycle.isEmpty()) {
                    break;
                }
            }
        }
//        writer.println("Edges in cycle: ");
//        for(Pair p : edgesInCycle) {
//            writer.println(p);
//        }
        if(edgesInCycle.isEmpty()) {
            writer.println("YES");
        }
        else {
            for(Pair p : edgesInCycle) {
                ignoredu = p.x;
                ignoredv = p.y;
                if(check()) {
                    writer.println("YES");
                    System.exit(0);
                }
            }
            writer.println("NO");
        }
    }
    static boolean dfs1(int v, Stack<Integer> st) {
        vis[v] = true;
        inStack[v] = true;
        st.add(v);
        for(int e : adj[v]) {
            if(!vis[e]) {
                if(!dfs1(e, st)) {
                    return false;
                }
            }
            else if(inStack[e]) {
                Stack<Integer> removed = new Stack<>();
                edgesInCycle.add(new Pair(v, e));
                int prev = v;
                removed.add(st.pop());
                while(!st.isEmpty()) {
                    int x = st.pop();
                    removed.add(x);
                    edgesInCycle.add(new Pair(x, prev));
                    if(x==e) {
                        break;
                    }
                    else {
                        prev = x;
                    }
                }
                while(!removed.isEmpty()) {
                    st.add(removed.pop());
                }
                return false;
            }
        }
        st.pop();
        inStack[v] = false;
        return true;
    }
    static boolean check() {
        vis = new boolean[n+1];
        inStack = new boolean[n+1];
        for(int i=1;i<=n;++i) {
            if(!vis[i]) {
                if(!dfs2(i)) {
                    return false;
                }
            }
        }
        return true;
    }
    static boolean dfs2(int v) {
        vis[v] = inStack[v] = true;
        for(int e : adj[v]) {
            if(ignoredu==v && ignoredv==e) {
                continue;
            }
            if(!vis[e]) {
                if(!dfs2(e)) {
                    return false;
                }
            }
            else if(inStack[e]) {
                return false;
            }
        }
        inStack[v] = false;
        return true;
    }
    static class Pair {
        int x,y;
        Pair(int x, int y) {
            this.x = x;
            this.y = y;
        }
        public String toString() {
            return "{" + x+ "," + y + "}";
        }
    }
}