#include<bits/stdc++.h>
using namespace std;

typedef pair<int,int> PII;
const int N = 150010;
int h[N],e[N],ne[N],w[N],idx;   //dist,st里装的是真正编号，w里装的是索引
int dist[N];
bool st[N];
int n,m;

void add(int a,int b,int c)
{
    e[idx]=b,w[idx]=c,ne[idx]=h[a],h[a]=idx++;
}

int dijkstra()
{
    memset(dist,0x3f,sizeof dist);
    priority_queue<PII,vector<PII>,greater<PII>> q;
    q.push({0,1});
    dist[1]=0;

    while(q.size())
    {
        PII t=q.top();
        q.pop();
        if(st[t.second]) continue;
        st[t.second]=true;

        for(int i=h[t.second];i!=-1;i=ne[i])
        {
            int j=e[i];
            if(dist[j]>dist[t.second]+w[i])
            {
                dist[j]=dist[t.second]+w[i];
                q.push({dist[j],j});
            }
        }
    }
    return dist[n];
}

int main()
{
    memset(h,-1,sizeof h);
    cin>>n>>m;
    while(m--)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        add(a,b,c);
    }
    int res=dijkstra();
    if(res==0x3f3f3f3f)
    {
        cout<<"-1";
        return 0;
    }
    else cout<<res;
}