#include <bits/stdc++.h>
using namespace std;
// x^y≡x^(y%(p-1))mod p
// but there is a condition that x needs to be coprime to p
///assic value of ('0'-'9') is(48 - 57) and (a-z) is (97-122) and (A-Z) is(65-90) and 32 for space
typedef long long int ll;
typedef pair<ll, ll> pii;
typedef vector<pii> vii;
#define  pb push_back
#define f(i,a,b) for(ll i=a;i<b;i++)
#define fo(i,a,b) for(ll i = a; i<=b;i+=1)
#define rf(i,a,b)  for(ll i=a;i>=b;i--)
#define vll vector<ll>
#define tests() int test_cases ; cin >> test_cases ; while(test_cases--)
#define ub upper_bound
#define lb lower_bound
#define all(v) v.begin(),v.end()
#define MAXN 100010
#define MOD 1000000007
#define mod 998244353
#define deb(x) cout << '>' << #x << ':' << x << endl;
#define sp " "
#define MS(x,y) fill_n(*x, sizeof x / sizeof **x, y);
#define INF 1000000000000000000
ll power(ll x, ll y,ll p)
{
    ll res = 1;     // Initialize result
    x = x % p;
    if (y==0)return 1;
    if(x==0)return 0;
    while (y > 0)
    {
        if (y & 1)
            res = (res*x) % p;
        y = y>>1; // y = y/2
        x = (x*x) % p;  // Change x to x^2
    }
    return res;
}
int gcd(int a, int b) { if (a == 0)return b;return gcd(b % a, a);}

ll modinv(ll a,ll p){return power(a,p-2,p);}

int solve(){
    ll n,m;
    cin>>n>>m;
    tuple<int,int,int> tup[m];
    tuple<int,int,int> rev[m];
    f(i,0,m){
        int a,b,c;
        cin>>a>>b>>c;
        tup[i] = make_tuple(a,b,-c);
        rev[i] = make_tuple(b,a,-c);
    }
    bool f1 = false,f2 = false;
    ll dist[n+1];
    fo(i,1,n){
        dist[i] = INF;
    }
    dist[1] = 0;
    fo(i,1,n-1){
        fo(j,0,m-1){
            ll u,v,w;
            tie(u,v,w) = tup[j];
            dist[v] = min(dist[v], dist[u]+w);
        }
    }
    fo(j,0,m-1){
        ll u,v,w;
        tie(u,v,w) = tup[j];
        if (dist[v]>dist[u]+w)
        {
            dist[v] = dist[u]+w;
            if (dist[v]<=1e9*5000)
            {
                f1 = true;
            }
        }
    }
    ll store = dist[n];
    fo(i,1,n){
        dist[i] = INF;
    }
    dist[n] = 0;
    fo(i,1,n-1){
        fo(j,0,m-1){
            ll u,v,w;
            tie(u,v,w) = rev[j];
            if (dist[v]>dist[u]+w)
            {
                dist[v] = min(dist[v], dist[u]+w);
            }
        }
    }
    fo(j,0,m-1){
        ll u,v,w;
        tie(u,v,w) = rev[j];
        if (dist[v]>dist[u]+w)
        {
            dist[v] = dist[u]+w;
            if (dist[v]<=1e9*5000)
            {
                f2 = true;
            }
        }
    }
    if (f1 and f2)
    {
        cout<<-1<<endl;
        return 0;
    }
    else {
        cout<<-store<<endl;
        return 0;
    }
    return 0;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL);



    // #ifndef ONLINE_JUDGE
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    // #endif



    // tests(){solve();}
    solve();
    return 0;
}