#include<bits/stdc++.h>
#define int long long
#define endl "\n"
#define made return 0;
#define by
#define bowen 
using namespace std;
int g[1510][1510];
signed main()
{   
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    // freopen("BFS.in","r",stdin);
    // freopen("BFS.out","w",stdout);
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n;j++)
        {
            if(i==j) g[i][j]=0;
            else g[i][j]=-1;
        }
    }
    while(m--)
    {
        int x,y,w;
        cin>>x>>y>>w;
        if(w>g[x][y]) g[x][y]=w;
    }
    for(int k=1;k<=n;k++)
    {
        for(int i=1;i<=n;i++)
        {
            if(g[i][k]!=-1)
            {
                for(int j=1;j<=n;j++)
                {
                    if(g[k][j]!=-1)
                    {
                        if(g[i][k]+g[k][j]>g[i][j]) g[i][j]=g[i][k]+g[k][j];
                    }
                }
            }
        }
    }
    cout<<g[1][n];
    made by bowen;
}

WA#1和#2，求条，悬关。