#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
typedef pair<int,int> PII;
const int N=1e6+10;
int n,m;
int e[N],h[N],ne[N],w[N],dist[N],idx;
bool st[N];
void add(int a, int b, int c)
{
    e[idx]=b,ne[idx]=h[a],w[idx]=c,h[a]=idx++;
}

int dijstra()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    priority_queue<PII,vector<PII>,greater<PII>> heap;
    heap.push({0,1});
    while(!heap.empty())
    {
        auto t=heap.top();heap.pop();
        int ver=t.second;
        if(st[ver])continue;
        st[ver]=true;
        for(int j=h[ver];j!=-1;j=ne[j])
        {
            int i=e[j];
            if(dist[i] > dist[ver] + w[j])
            {
                dist[i]=dist[ver]+w[j];
                heap.push({dist[i],i});
            }
        }
    }
    if(dist[n]==0x3f3f3f3f) return -1;
    return dist[n];
}

int main()
{
    cin>>n>>m;
    memset(h,-1,sizeof h);
    for(int i=0;i<m;++i)
    {
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        add(a,b,c);
    }
    cout<<dijstra()<<endl;
    return 0;
}