//author : ainunsy1
#include <bits/stdc++.h>
#define forn(i,a,b) for(int i=a; i<=b; i++)
#define ford(i,a,b) for(int i=a; i>=b; i--)
#define fi first
#define se second
using namespace std;
typedef long long ll;
const int MX=5e3+5;
ll n,m,dist[MX],vis[MX];
vector<tuple<ll,ll,ll>>v;
vector<ll> adj[MX];
void dfs(int i){
    vis[i]=1;
    for(auto j:adj[i])
        if(!vis[j])
            dfs(j);
}
void solve(){
    dist[1]=0;
    cin>>n>>m;
    forn(i,2,n)
        dist[i]=LLONG_MIN;
    forn(i,1,m){
        ll a,b,w;
        cin>>a>>b>>w;
        adj[a].push_back(b);
        v.push_back({a,b,w});
    }
    forn(i,1,m){
        for(auto [a,b,w]:v){
            if(dist[a]!=LLONG_MIN && dist[b]<dist[a]+w)
                dist[b]=dist[a]+w;
        }
    }
    bool ada=false,gaada=true;
    for(auto [a,b,w]:v){
        if(dist[a]!=LLONG_MIN && dist[b]<dist[a]+w){
            memset(vis,0,sizeof(vis));
            dfs(a);
            ada|=(!vis[n]);
            gaada&=(vis[n]);
        }
    }
    if(ada || gaada)
        cout<<dist[n]<<"\n";
    else
        cout<<"-1\n";
}
int main(){
    ios::sync_with_stdio(0); cin.tie(0);
    int tc=1;
    // cin>>tc;
    forn(i,1,tc){
        solve();
    }
}