import java.util.*;
class Main{
    static int N=200010;
    static int idx=0;
    static int[] h=new int[N],e=new int[N],ne=new int[N],w=new int[N];
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int m=sc.nextInt();
        Arrays.fill(h,-1);
        for(int i=0;i<m;i++){
            add(sc.nextInt(),sc.nextInt(),sc.nextInt());
        }

        System.out.println(dij(n));
    }

    static void add(int from ,int to,int dist){//添加一条边
        e[idx]=to;//出边指向to点
        w[idx]=dist;//边距离
        ne[idx]=h[from];//头插from点的邻接表
        h[from]=idx++;
    }

    static int dij(int n){//n是点的数量
        PriorityQueue<int[]> q=new PriorityQueue<int[]>(new Comparator<int[]>(){//小根堆
            public int compare(int[] o1,int[] o2){
                return o1[0]-o2[0];
            }
        });
        q.offer(new int[]{0,1});// (距离,点编号)
        boolean[] status=new boolean[n+1];//状态，表示下标编号的点已经求得到原点的最短距离
        int[] dist=new int[n+1];//下标编号的点到原点最小距离
        Arrays.fill(dist,0x3f3f3f3f);
        dist[1]=0;
        int[] cur;
        int distance,point;
        while(q.size()>0){
            cur=q.poll();
            distance=cur[0];
            point=cur[1];
            if(status[point]){
                continue;
            }
            status[point]=true;
            for(int i=h[point];i!=-1;i=ne[i]){
                int j=e[i];
                if(dist[j] > distance+w[i]){
                    dist[j]=distance+w[i];
                    q.offer(new int[]{dist[j],j});
                }
            }
        }
        return dist[n]==0x3f3f3f3f?-1:dist[n];
    }
}