#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin (), x.end ()
#define ott(i,l,r) for (int i = l; i <= r; i ++)
#define tto(i,l,r) for (int i = r; i >= l; i --)
using namespace std;
using ll = long long;
int read () {
	int x = 0; bool f = 0; char c = getchar ();
	while (!isdigit (c)) f |= (c == '-'), c = getchar ();
	while (isdigit (c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar ();
	if (f) x = -x; return x;
}
const int N = 2200, mod = 1e9 + 7, inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
int T, n, m;
vector <array <int, 3> > a;
ll dis[N];
bool check (ll val) {
	memset (dis, -0x3f, sizeof dis); dis[n] = val;
	ott (i, 1, n)
		for (auto [u, v, w] : a) 
			if (dis[u] >= 0 && dis[u] + w >= 0 && dis[v] < dis[u] + w)
				dis[v] = dis[u] + w;
	for (auto [u, v, w] : a)
		if (dis[u] >= 0 && dis[u] + w >= 0 && dis[v] < dis[u] + w)
			dis[v] = INF;
	ott (i, 1, n)
		for (auto [u, v, w] : a) 
			if (dis[u] == INF)
				dis[v] = INF;
	return dis[1] >= 0;
}
int main () {
	n = read (), m = read ();
	ott (i, 1, m) {
		int x = read (), y = read (), z = read ();
		a.pb ({y, x, -z});
	}
	ll l = 0, r = INF, res = -1;
	while (l <= r) {
		ll mid = l + r >> 1;
		if (check (mid)) r = mid - 1, res = mid;
		else l = mid + 1;
	}
	printf ("%lld\n", res);
	return 0;
}