#include <iostream>
using namespace std;
 
int main() 
{
	int n, m, i = 0, k = 0;
	bool p = true;
	cin >> n >> m;
	int v[m], g[m];
	for (int i = 0; i < m; i ++)
	{
		cin >> v[i] >> g[i];
	}
	while (p)
	{
		for (int j = i+1; j < m; j ++)
		{
			if ( (v[i] == v[j]) && (g[i] == g[j]) ) 
			{ 
				k++; 
				cout<<"YES"<<endl; 
				p=false; //Выход из цикла.
			}
		}
		i ++;
		if (i == m) break; //Условие окончания цикла.
	}
	if (k == 0) cout<<"NO"<<endl;
	return 0;
}

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MyA0CjEgMiAKMiAzCjMgMSAKMyAx

3 4
1 2 
2 3
3 1 
3 1