#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int N=1e5+10;
typedef pair<int,int>PII;
int h[N],idx,w[N],e[N],ne[N];
int dist[N];
bool st[N];
int n,m;
void add(int x,int y, int z)
{
    e[idx]=y,w[idx]=z,ne[idx]=h[x],h[x]=idx++;
}
int dijkstra()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    priority_queue<PII,vector<PII>,greater<PII>>heap;//升序  顶部最小值
    heap.push({0,1});
    while(heap.size())
    {
        auto t=heap.top();
        heap.pop();
        int ver=t.second,distance=t.first;
        if(st[ver])continue;
        st[ver]=true;
        for(int i=h[ver];i!=-1;i=ne[i])
        {
            int j=e[i];
            if(dist[j]>distance+w[i])
            {
                dist[j]=distance+w[i];
                heap.push({dist[j],j});
            }
        }
    }
    if(dist[n]==0x3f3f3f3f)return -1;
    return dist[n];

}
int main()
{
    cin>>n>>m;  
    memset(h,-1,sizeof h);
    while(m--)
    {
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        add(x,y,z);

    }
    cout<<dijkstra()<<endl;
    return 0;
}