#include <iostream>
#include <vector>
#include <algorithm>
#include <climits>

using namespace std;

struct edge
{
    int to, len;
};

vector<edge> G[1501];
int n, m;
long long record[1501];

long long DFS(int x)
{
    if (x == n)
        return 0;
    if (record[x] > INT_MIN)
        return record[x];
    for (auto e : G[x])
        record[x] = max(record[x], DFS(e.to) + e.len);
    return record[x];
}

int main()
{
    ios::sync_with_stdio(false);
    fill(record, record + 1501, INT_MIN);
    cin >> n >> m;
    while (m--)
    {
        int u, v, w;
        cin >> u >> v >> w;
        G[u].push_back({v, w});
    }
    long long ans = DFS(1);
    if (ans > INT_MIN)
        cout << ans;
    else
        cout << -1;
    cout << flush;
    return 0;
}