1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 #include <cstring>
 5 #include <queue>
 6 #include <vector>
 7 using namespace std;
 8 const int INF = 0x3f3f3f3f;
 9 struct edge{
10     int to,cost;
11 };
12 typedef pair<int,int> p;
13 int V;
14 vector<edge> G[105];
15 int d[105];
16 void dijkstra(int s){
17     priority_queue<p,vector<p>,greater<p> > q;
18     memset(d,INF,sizeof(d));
19     d[s] = 0;
20     q.push(p(0,s));
21     while(!q.empty()){
22         p cur = q.top(); q.pop();
23         int v = cur.second;
24         if(d[v]<cur.first) continue;
25         for(int i = 0; i<G[v].size(); i++){
26             edge e = G[v][i];
27             if(d[e.to]>d[v]+e.cost){
28                 d[e.to] = d[v] + e.cost;
29                 q.push(p(d[e.to],e.to));
30             }
31         }
32     }
33 }
34 void solve(){
35     int n,m;
36     while(scanf("%d%d",&n,&m) == 2&&n&&m){
37             for(int i = 0; i<105; i++) G[i].clear();
38         for(int i = 0; i<m; i++)
39         {
40             int A,B,C;
41             scanf("%d%d%d",&A,&B,&C);
42             G[A].push_back((edge){B,C});
43             G[B].push_back((edge){A,C});
44         }
45         dijkstra(1);
46         printf("%d\n",d[n]);
47     }
48 }
49 int main()
50 {
51     solve();
52     return 0;
53 }