#include<bits/stdc++.h>
#define inf 1000000000
#define intt long long

using namespace std ;

intt a , b , weight[11112][11112] , n , m , w ,adj[11112][11112] , d[11112] , p[11112] ;

void initialize ( int s )
{

    for ( intt i = 1 ; i <= n ; i ++ )
    {

        d[i] = inf ;

        d[s] = 0 ;

    }

}

void relax ( intt u , intt v )
{

    if ( d[v] > d[u] + weight[u][v] )
    {

        d[v] = d[u] + weight[u][v] ;

        p[v] = u ;

    }

}

void Bellman_Ford ( int s )
{

    initialize ( s ) ;

    for ( intt k = 1 ; k < n ; k ++ )
    {

        for ( intt i = 1 ; i <= n ; i ++ )

            for ( intt j = 1 ; j <= n ; j ++ )
            {
                if ( adj[i][j] == 1 )

                relax ( i , j ) ;

        }

    }

}

bool negativeCycle ()


    for ( intt i = 1 ; i <= n ; i ++ )
    {

        for ( intt j = 1 ; j <= n ; j ++ )
        {

            if ( adj[i][j] == 1 && d[j] > d[i] + weight[i][j] )

                return true ;

        }

    }

    return false ;

}

int main ()
{

    cin >> n >> m ;

    while ( m -- )
    {

        cin >> a >> b >> w ;

        if ( adj[a][b] == 1 )
        {

            weight[a][b] = min ( w , weight[a][b] ) ;

            continue ;

        }

        adj[a][b] = 1 ;

        weight[a][b] = w ;

    }

    Bellman_Ford ( 1 ) ;

    if ( negativeCycle () == true ) cout << "yes" << endl ;

    else cout << "no" << endl ;

    return 0 ;

}