#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;
vector<int> g[maxn];
int dfn[maxn];
int low[maxn],num;
int in[maxn];
int s[maxn],top;
int cnt;
int c[maxn];
void tarjan(int u)
{
    dfn[u] = low[u] = ++num;
    s[++top] = u;
    in[u] = 1;
    for(int &v : g[u])
    {
        if(!dfn[v])
        {
            tarjan(v);
            low[u] = min(low[u],low[v]);
        }
        else if(in[v]) low[u] = min(low[u],dfn[v]);
    }
    if(dfn[u] == low[u])
    {
        cnt++;
        int v;
        do
        {
            v = s[top--];
            c[v] = cnt;
            in[v] = 0;
        }
        while(v != u);
    }
}
struct node
{
    int u,v,w;
};
vector<node> xz[maxn];
i64 ck(int d)
{
    vector<int> b;
    for(node &a : xz[d])
    {
        b.push_back(a.u);
        b.push_back(a.v);
    }
    if(b.size() == 0) return mod;
    sort(b.begin(),b.end());
    b.erase(unique(b.begin(),b.end()),b.end());
    int len = b.size();
    vector<vector<pair<int,int>>> v(len+1);
    for(node &a : xz[d])
    {
        a.u = lower_bound(b.begin(),b.end(),a.u) - b.begin() + 1;
        a.v = lower_bound(b.begin(),b.end(),a.v) - b.begin() + 1;
        v[a.u].push_back({a.v,a.w});
    }
    i64 ans = mod;
    for(node &a : xz[d])
    {
        vector<int> dis(len+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);
    }
    return ans;
}
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});
        g[x].push_back(y);
    }
    for(int i = 1; i <= n; ++i) if(!dfn[i]) tarjan(i);
    for(node &a : e)
    {
        if(c[a.u] == c[a.v]) xz[c[a.u]].push_back(a);
    }
    for(int i = 1; i <= cnt; ++i) ans = min(ans,ck(i));
    if(ans == mod) cout << -1 << endl;
    else cout << ans << endl;
    return 0;
}