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using System;
using System.Collections.Generic;


namespace ConsoleApplication11
{
    class Program
    {
         public static List<int>[] g ;
        public static int[] used;
        public static int color = 0;
        public static void dfs(int v)
        {
            used[v] = color;
            foreach (int to in g[v])
            {
                if (used[to] == 0 )
                {
                    dfs(to);
                }
            }
        }
        static void Main(string[] args)
        {
            int n, m;
            string[] s = Console.ReadLine().Split();
            n = int.Parse(s[0]);
            m = int.Parse(s[1]);
            g = new List<int>[n];
            used = new int[m];
            for (int i = 0; i < n; i++)
                g[i] = new List<int>();
            {

            }
            for (int i = 0; i < m; i++)
            {
                s = Console.ReadLine().Split();
                int from=int.Parse(s[0]);
                int to = int.Parse(s[1]);
                from--;
                to--;
                g[from].Add(to);
                g[to].Add(from);
            }
            for (int i = 0; i < n; i++)
            {
                if (used[n]==0)
                {
                    color++;
                    dfs(i);
                }
            }

            Console.WriteLine(color == 1? "yes" : "no" );
        }




        //static void dfs(int v)
        //{
        //    used[v] = 1;

        //    for (int i = 1; i <= n; i++)

        //        if (g[v,i] && !used[i]) dfs(i);

        //}


    }
}

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