/* Problem URL: https://cses.fi/problemset/task/1673 */

#include <bits/stdc++.h>

#include <algorithm>

using namespace std;

#define V vector

#define rmin(a, b) a = min(a, b)
#define rmax(a, b) a = max(a, b)

#define rep(i, lim) for (int i = 0; i < (lim); i++)
#define nrep(i, s, lim) for (int i = s; i < (lim); i++)

#define repv(i, v) for (auto &i : (v))
#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
#define sortv(v) sort(v.begin(), v.end())
#define all(v) (v).begin(), (v).end()

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vvvvi = vector<vvvi>;

using ll = long long;

using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vvvvl = vector<vvvl>;

template<class v>
auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
    os << vec[0];
    for (size_t i = 1; i < vec.size(); i++) {
        os << ' ' << vec[i];
    }
    os << '\n';
    return os;
}

template<class v>
auto operator>>(istream &is, vector<v> &vec)->istream& {
    for (auto &i : vec) {
        is >> i;
    }
    return is;
}

template<class v>
auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
    for (auto &i : vec) {
        os << i[0];
        for (size_t j = 1; j < i.size(); j++) {
            os << ' ' << i[j];
        }
        os << '\n';
    }
    return os;
}

template<class v>
auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
    for (auto &i : vec) {
        for (auto &j : i) {
            is >> j;
        }
    }
    return is;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;

    V<tuple<int, int, ll>> edges;
    V<V<pair<ll, int>>> graph(n);

    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        a--, b--;

        edges.emplace_back(a, b, -c);
        graph[a].emplace_back(b, c);
    }

    V<bool> reachable(n, false);
    V<bool> vis(n, false);

    reachable.back() = true;

    function<bool(int)> dfs = [&](int i) -> bool {
        vis[i] = true;

        for (auto [j, c] : graph[i]) {
            if (reachable[j]) {
                reachable[i] = true;
            }

            if (vis[j]) {
                continue;
            }

            if (dfs(j)) {
                reachable[i] = true;
            }
        }

        return reachable[i];
    };

    dfs(0);

    auto bellman = [&]() -> ll {
        ll inf = INT64_MAX >> 1;
        vl dis(n, inf);
        dis[0] = 0;

        rep(i, n - 1) {
            for (auto [a, b, c] : edges) {
                if (dis[a] < inf) {
                    rmin(dis[b], dis[a] + c);
                }
            }
        }
        
        for (auto [a, b, c] : edges) {
            if (dis[a] < inf && dis[b] > dis[a] + c) {
                if (reachable[b]) {
                    return -1;
                }
                dis[b] = dis[a] + c;
            }
        }

        return -dis.back();
    };

    cout << bellman() << '\n';
}