using namespace std;
struct node
{
    int x, w;
};
int n, m, mx = 0, k;
vector<node> v[maxn];
int vis[maxn] = {0};
void dfs(int x, int s)
{
    if (s > mx) mx = s, k = x;
    for (int i = 0; i < v[x].size(); i++) if (!vis[v[x][i].x])
    {
        vis[v[x][i].x] = 1;
        dfs(v[x][i].x, s + v[x][i].w);
        vis[v[x][i].x] = 0;
    }
}
int main ()
{
    while(scanf("%d%d", &n, &m) != EOF)
    {
        int x, y;
        node tmp;
        char ch;
        for (int i = 0; i <= n; i++) v[i].clear();
        while(m--)
        {
            scanf("%d%d%d %c", &x, &y, &tmp.w, &ch);
            tmp.x = y, v[x].push_back(tmp);
            tmp.x = x, v[y].push_back(tmp);
        }
        mx = 0;
        mem(vis, 0), vis[1] = 1;
        dfs(1, 0);
        mem(vis, 0), vis[k] = 1;
        dfs(k, 0);
        cout<<mx<<endl;
    }
    return 0;
}