1 #include<algorithm>
 2 #include<iostream>
 3 #include<cstdlib>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<vector>
 7 #include<queue>
 8 #include<map>
 9 using std::map;
10 using std::cin;
11 using std::cout;
12 using std::endl;
13 using std::find;
14 using std::sort;
15 using std::pair;
16 using std::vector;
17 using std::multimap;
18 using std::priority_queue;
19 #define pb(e) push_back(e)
20 #define sz(c) (int)(c).size()
21 #define mp(a, b) make_pair(a, b)
22 #define all(c) (c).begin(), (c).end()
23 #define iter(c) decltype((c).begin())
24 #define cls(arr,val) memset(arr,val,sizeof(arr))
25 #define cpresent(c, e) (find(all(c), (e)) != (c).end())
26 #define rep(i, n) for (int i = 0; i < (int)(n); i++)
27 #define tr(c, i) for (iter(c) i = (c).begin(); i != (c).end(); ++i)
28 const int N = 11000;
29 typedef unsigned long long ull;
30 struct P {
31     int w, v;
32     P(int i = 0, int j = 0) :w(i), v(j) {}
33     inline bool operator<(const P &a) const {
34         return w > a.w;
35     }
36 };
37 struct Node { int to, w, next; };
38 int n, m;
39 struct Dijkstra {
40     Node G[N];
41     int tot, dist[N], head[N];
42     inline void init() {
43         tot = 0;
44         cls(head, -1), cls(dist, 0x3f);
45     }
46     inline void add_edge(int u, int v, int w) {
47         G[tot] = { v, w, head[u] }; head[u] = tot++;
48     }
49     inline void built(int m) {
50         int u, v, w;
51         rep(i, m) {
52             scanf("%d %d %d", &u, &v, &w);
53             add_edge(u, v, w), add_edge(v, u, w);
54         }
55     }
56     inline void dijkstra(int s) {
57         dist[s] = 0;
58         priority_queue<P> q;
59         q.push(P(0, s));
60         while (!q.empty()) {
61             P t = q.top(); q.pop();
62             int u = t.v;
63             if (dist[u] < t.w) continue;
64             for (int i = head[u]; ~i; i = G[i].next) {
65                 int &w = dist[G[i].to];
66                 if (w > dist[u] + G[i].w) {
67                     w = dist[u] + G[i].w;
68                     q.push(P(w, G[i].to));
69                 }
70             }
71         }
72         printf("%d\n", dist[n]);
73     }
74 }go;
75 int main() {
76 #ifdef LOCAL
77     freopen("in.txt", "r", stdin);
78     freopen("out.txt", "w+", stdout);
79 #endif
80     while (~scanf("%d %d", &n, &m), n + m) {
81         go.init();
82         go.built(m);
83         go.dijkstra(1);
84     }
85     return 0;
86 }