#include<bits/stdc++.h>
using namespace std;
const int N = 1510, M = 5e4+10;
struct edge{
    int a,b,c;
}edges[M];
int n,m;
int dist[N],backup[N];

void bell(){
    fill_n(dist,N,INT_MIN);
    dist[1] = 0;
    for(int i = 0; i < n; i++){
        memcpy(backup,dist,sizeof(dist));
        for(int j = 0; j < m; j++){
            auto e = edges[j];
            dist[e.b] = max(dist[e.b],backup[e.a]+e.c);
        }
    }
}

int main(){
    cin>>n>>m;
    for(int i = 0; i < m; i++){
        int u,v,w;
        cin>>u>>v>>w;
        edges[i] = {u,v,w};
    }
    bell();
    if(dist[n] < INT_MIN/2) printf("-1");
    else printf("%d",dist[n]);
    return 0;
}