#include <bits/stdc++.h>
using namespace std;
#define int long long
int ans[2001],fr[150001],to[150001],w[150001],n,m;
signed main(){
	cin >> n >> m;
	memset(ans,-1,sizeof ans);
	memset(vis,63,sizeof vis);
	for(int i = 1; i <= m; i++){
		cin >> fr[i] >> to[i] >> w[i];
	}
	ans[1] = 0;
	for(int i = 1; i < n; i++){
		for(int j = 1; j <= m; j++){
			if(ans[to[j]] < ans[fr[j]] + w[j]) ans[to[j]] = ans[fr[j]] + w[j];
		}
	}
	cout << ans[n];
	return 0;
}