#include<iostream>
#include<cstring>
#include<queue>
#include<algorithm>

using namespace std;

const int N=1e6+10;
typedef pair<int,int> PII;

int h[N],w[N],ne[N],e[N],idx;
int n,m;
int dist[N];
bool st[N];

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);
    dist[1]=0;
    priority_queue<PII,vector<PII>,greater<PII>> heap;
    heap.push({0,1});
    while(heap.size()){
        auto t=heap.top();
        heap.pop();
        int ver=t.second,distace=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]>dist[ver]+w[i]){
                dist[j]=dist[ver]+w[i];
                heap.push({dist[j],j});
            }
        }
    }
    if(dist[n]==0x3f3f3f3f)return -1;
    return dist[n];
}
int main(){
    scanf("%d%d",&n,&m);
    memset(h,-1,sizeof h);
    while(m--){
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        add(a,b,c);
    }
    cout<<dijkstra()<<endl;
    return 0;
}