#include <fstream>
#include <vector>
#pragma comment (linker, "/STACK:64000000")

using namespace std;

int m, n, fr, to;
vector <vector <int>> g;
vector <int> clr;
vector <int> tmp;
bool cycle = false;

void dfs (int v)
{
    clr[v] = 1;
    for (size_t i = 0; i < g[v].size(); ++i)
    {
        int a = g[v][i];
        if (clr[a] == 0)
        {
            clr[a] = 1;
            dfs(a);
        }
        if (clr[a] == 1)
            cycle = true;

    }
    tmp.push_back(v);
    clr[v] = 2;
}

void topological_sort()
{
    for (int i = 0; (i < n)&&(cycle == false); i++)
        if (clr[i] == 0)
            dfs(i);

    reverse(tmp.begin(), tmp.end());
}

bool is_gam()
{
    bool res = false;
   for(int i = 0; i < n - 1; i++)
   {
      int a = tmp[i];
      int b = tmp[i + 1];
      for(int j = 0; j < g[a].size(); j++)
      {
         if(g[a][j] == b)
            res = true;
      }
      if(!res)
         return false;
      res = false;
   }
   return true;
}

int main()
{
    ifstream in("hamiltonian.in");
    ofstream out("hamiltonian.out");

    in >> n >> m;

    g.resize(n);
    clr.resize(n);

    for (int i = 0; i < m; i++)
    {
        in >> fr >> to;
        g[fr - 1].push_back(to - 1);
    }
    topological_sort();

    if (is_gam() == true)
        out << "YES";
    else
        out << "NO";
    return  0;
}