using System;
using System.Collections;
using System.Collections.Generic;

// (づ°ω°)づﾐe★゜・。。・゜゜・。。・゜☆゜・。。・゜゜・。。・゜

namespace TASK
{
	class MainClass
	{
		public static List<int> FindCycle(int[] parent, int u, int v)
		{
			List<int> Cycle = new List<int>();
			while (u != v)
			{
				Cycle.Add(u);
				u = parent[u];
			}
			Cycle.Add(v);
			Cycle.Reverse();
			return Cycle;
		}

		public static List<int> dfs(List<int>[] Graph, int[] used, int [] parent , int v , List<int> z)
		{
			if (z.Count > 0)
				return z;
			used[v] = 1;
			for (int i = 0; i < Graph[v].Count; ++i)
			{
				if (z.Count > 0)
					return z;
				int to = Graph[v][i];
				parent[to] = v;
				if (used[to] == 1)
				{
					z = FindCycle(parent, v, to);
					return z;
				}
				if (used[to] == 0)
                	dfs(Graph, used, parent, to, z);
			}
			used[v] = 2;
			return z;
		}

		public static int check(List<int>[] Graph, int[] used, int v)
		{
			int ans = 0;
			used[v] = 1;
			for (int i = 0; i < Graph[v].Count; ++i)
			{
				int to = Graph[v][i];
				if (used[to] == 1)
				{
					return Math.Max(ans, 1);
				}
				if (used[to] == 0)
					check(Graph, used, to);
			}
			used[v] = 2;
			return ans;
		}

		public static void Main(string[] args)
		{
			int N = Reader.NextInt();
			int m = Reader.NextInt();
			List<int>[] Graph = new List<int>[N + 1];
			for (int i = 0; i < m; ++i)
			{
				int from = Reader.NextInt();
				int to = Reader.NextInt();
				if (Graph[from] == null)
                    Graph[from] = new List<int>();
				if (Graph[to] == null)
					Graph[to] = new List<int>();
				Graph[from].Add(to);
			}
			bool flag = false;
			int[] used = new int[N + 1];
			int[] parent = new int[N + 1];
			for (int i = 0; i <= N; ++i)
				parent[i] = i;
			List <int> Cycle = new List<int>();
			for (int i = 1; i <= N; ++i)
			{
				if (used[i] == 0 && flag == false)
				{
					List<int> z = new List<int>();
					List<int> res = dfs(Graph, used, parent, i , z);
					if (res.Count != 0)
					{
						Cycle = res;
						flag = true;
					}
				}
			}
			if (!flag)
			{
				Console.WriteLine("YES");
			}
			else
			{
				int ans = 0;
				for (int i = 1; i <= Cycle.Count; ++i)
				{
					int x = Cycle[i - 1], y = Cycle[i];
					Graph[x].Remove(y);
					for (int j = 1; j <= N; ++j)
						used[i] = 0;
					bool ok = false;
					for (int j = 1; j <= N; ++j)
					{
						if (used[j] == 0 && ok == false)
						{
							int T = check(Graph, used, j);
							ans = Math.Max(ans, T);
						}
					}
					Graph[x].Add(y);
				}
				Console.WriteLine(ans == 1 ? "YES" : "NO");
			}

		}

		class Reader
		{
			public static int NextInt()
			{
				int cnt = 0, sign = 1;
				char ch = Convert.ToChar(Console.Read());
				while (!(ch >= '0' && ch <= '9') && ch != '-')
					ch = Convert.ToChar(Console.Read());
				if (ch == '-')
				{
					sign = -1;
					ch = Convert.ToChar(Console.Read());
				}
				while (ch >= '0' && ch <= '9')
				{
					int t = Convert.ToInt32(ch);
					cnt = cnt * 10 + ch - '0';
					ch = Convert.ToChar(Console.Read());
				}
				return cnt * sign;
			}
			public static long NextLong()
			{
				long cnt = 0, sign = 1;
				char ch = Convert.ToChar(Console.Read());
				while (!(ch >= '0' && ch <= '9') && ch != '-')
					ch = Convert.ToChar(Console.Read());
				if (ch == '-')
				{
					sign = -1;
					ch = Convert.ToChar(Console.Read());
				}
				while (ch >= '0' && ch <= '9')
				{
					long t = Convert.ToInt64(ch);
					cnt = cnt * 10 + ch - '0';
					ch = Convert.ToChar(Console.Read());
				}
				return cnt * sign;
			}
		}
	}
}