#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define i64 long long
#define i128 __int128
#define int long long
#define endl '\n'
using namespace std;
const i64 mod = 1e18;
const int maxn = 3e5+10;
struct node {int u,v,w;};
signed main()
{
    IOS;
    int n,m;
    cin >> n >> m;
    vector<node> e;
    i64 ans = mod;
    for(int i = 1; i <= m; ++i)
    {
        int x,y,z;
        cin >> x >> y >> z;
        if(x == y)
        {
            ans = min(ans,z);
            continue;
        }
        e.push_back((node){x,y,z});
    }
    vector<int> f(n+1);
    for(int i = 1; i <= n; ++i) f[i] = i;
    auto get = [&](auto self,int x) -> int
    {
        if(f[x] == x) return x;
        return f[x] = self(self,f[x]);
    };
    sort(e.begin(),e.end(),[&](node a,node b){return a.w < b.w;});
    vector<vector<pair<int,int>>> v(n+1);
    vector<node> qs;
    for(node &a : e)
    {
        int s1 = get(get,a.u);
        int s2 = get(get,a.v);
        if(s1 != s2)
        {
            v[a.u].push_back({a.v,a.w});
            f[s1] = s2;
        }
        else qs.push_back(a);
    }
    for(node &a : qs)
    {
        vector<int> dis(n+1,mod);
        dis[a.v] = 0;
        priority_queue<pair<int,int>> q;
        q.push({0,a.v});
        while(q.size())
        {
            int x = q.top().second;
            q.pop();
            for(auto [u,val] : v[x])
            {
                if(dis[u] > dis[x] + val)
                {
                    dis[u] = dis[x] + val;
                    q.push({-dis[u],u});
                }
            }
        }
        ans = min(ans,dis[a.u] + a.w);
    }
    if(ans == mod) cout << -1 << endl;
    else cout << ans << endl;
    return 0;
}