1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 using namespace std;
 5 #define N 250
 6 #define M 10005
 7 #define INF 0x1fffffff
 8 struct Edge{
 9     int to;
10     int w ;
11     int next;
12 }edge[M];
13 int Enct;
14 int head[N];
15 void init()
16 {
17     Enct = 0;
18     memset(head,-1,sizeof(head));
19 }
20 void add(int from , int to,int w)
21 {
22     edge[Enct].to= to;
23     edge[Enct].w = w;
24     edge[Enct].next = head[from];
25     head[from] = Enct++;
26     edge[Enct].to= from;
27     edge[Enct].w = w;
28     edge[Enct].next = head[to];
29     head[to] = Enct++;
30 }
31 int que[N];
32 bool inq[N];
33 int top;
34 int dis[N];
35 int n; 
36 int SPFA()
37 {
38     memset(inq,0,sizeof(inq));
39     for(int i =0 ;i <= n ;i++)
40         dis[i] = INF;
41     top = 0;
42     dis[1] = 0;
43     que[top++] = 1;
44     inq[1]=true;
45     for(int i = 0;i != top ;i = i+1%N)//队列不为空，注意i和top不是同时循环到下一次的
46     {
47         int u = que[i];
48         inq[u]=false;
49         for(int j = head[u] ; j!=-1 ;j = edge[j].next)
50         {
51             Edge e = edge[j];
52             if(dis[e.to]>dis[u]+e.w)
53             {
54                 dis[e.to] = dis[u]+e.w;
55                 if(inq[e.to]==false)
56                 {
57                     que[top++] = e.to;
58                     top %= N;//循环队列
59                     inq[e.to] = true;
60                 }
61             }
62         }
63     }
64     return dis[n];
65 }
66 int main()
67 {
68     int m ;
69     while(~scanf("%d %d",&n,&m) && (n!=0||m!=0))
70     {
71         init();
72         int s , t , w;
73         for(int i = 0 ;i < m ;i++)
74         {
75             scanf("%d%d%d",&s,&t,&w);
76             add(s,t,w);
77         }
78         printf("%d\n",SPFA());
79     }
80     return 0;
81 }