#include<bits/stdc++.h>
using namespace std;
#define int long long
int read()
{
    char ch = getchar();
    int x = 0,f = 1;
    while(ch < '0' || ch > '9')
    {
        if(ch == '-')f = -1;
        ch = getchar();
    }
    while(ch >= '0' && ch <= '9')
    {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x * f;
}
int a[2001][2001];
queue <int> q;
int rd[2001];
int dp[2001];
signed main()
{
	int n,m;
	n = read(),m = read();
	for(int i = 1;i <= m;i ++)
	{
		int x,y,z;
		x = read(),y = read(),z = read(); 
		a[x][y] = z;
		rd[y] ++;
	}
	memset(dp,128,sizeof(dp));
	for(int i = 1;i <= n;i ++)
	{
		if(rd[i] == 0)
		{
			q.push(i);
		}
	}
	while(!q.empty())
    {
		int x = q.front();
		q.pop();
		for(int i = 1;i <= n;i ++)
        {
			if(a[x][i])
            {
				rd[i] --;
				if(rd[i] == 0)
                {
					q.push(i);
				}
			}
		}
	}
	dp[1] = 0;
	q.push(1);
	while(!q.empty())
	{
		int x = q.front();
		q.pop();
		for(int i = 1;i <= n;i ++)
		{
			if(a[x][i] == 0)continue;
			dp[i] = max(dp[i],dp[x] + a[x][i]);
			rd[i] --;
			if(rd[i] == 0)
			{
				q.push(i);
			}
		}
	}
	if(dp[n] == INT_MIN)
	{
		cout<<-1;
		return 0;
	}
	cout<<dp[n];
	return 0;
}