#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const int N = 100005;
const int M = 2000005;
int father[N];
struct Edge
{
    int v,w,next;
} edge[M];
int head[N];
int n,m,tot;
void addEdge(int u,int v,int w,int &k)
{
    edge[k].v = v,edge[k].w = w,edge[k].next = head[u],head[u] = k++;
}
int _find(int x)
{
    if(x!=father[x]) father[x] = _find(father[x]);
    return father[x];
}
void init()
{
    tot = 0;
    for(int i=1; i<=n; i++)
    {
        father[i] = i;
        head[i] = -1;
    }
}
int dis[N];
bool vis[N];
bool used[N];
void bfs(int s)
{
    memset(vis,false,sizeof(vis));
    queue<int>q;
    q.push(s);
    vis[s] = true;
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        for(int k = head[u]; k!=-1; k=edge[k].next)
        {
            int w = edge[k].w,v = edge[k].v;
            if(!vis[v])
            {
                used[v] = true;
                vis[v] = true;
                q.push(v);
                dis[v] = max(dis[v],dis[u]+w);
            }
        }
    }

}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        if(n==0)
        {
            printf("0\n");
            continue;
        }
        init();
        bool flag = false;
        for(int i=1; i<=m; i++)
        {
            int u,v,w;
            scanf("%d%d%d",&u,&v,&w);
            addEdge(u,v,w,tot);
            addEdge(v,u,w,tot);
            if(!flag)
            {
                int ru = _find(u);
                int rv = _find(v);
                if(ru==rv) flag = true;
                else father[ru] = rv;
            }
        }
        if(flag)
        {
            printf("YES\n");
            continue;
        }
        memset(used,false,sizeof(used));
        int res = 0;
        for(int i=1; i<=n; i++)
        {
            if(used[i]) continue;
            int s=i,t;
            used[s] = true;
            memset(dis,0,sizeof(dis));
            bfs(s);
            int len = 0;
            for(int i=1; i<=n; i++)
            {
                if(dis[i]>len)
                {
                    len = dis[i];
                    t = i;
                }
            }
            memset(dis,0,sizeof(dis));
            bfs(t);
            int MAX = 0;
            for(int i=1; i<=n; i++)
            {
                MAX = max(dis[i],MAX);
            }
            res = max(res,MAX);

        }
        printf("%d\n",res);
    }
    return 0;
}