1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 
 5 int n,node[1010][1010],map[1010][1010],Min;
 6 const int INF=99999999;
 7 
 8 int floyd()
 9 {
10     for (int i=1; i<=n; i++)
11         for (int j=1; j<=n; j++)
12         {
13             node[i][j]=map[i][j];
14         }
15     Min=INF;
16     for (int k=1; k<=n; k++)
17     {
18         for (int i=1; i<=k; i++)
19             for (int j=1; j<i; j++)
20             {
21                 if (Min>node[i][j]+map[j][k]+map[k][i])
22                     Min=node[i][j]+map[j][k]+map[k][i];
23                 //cout<<Min<<endl;
24             }
25         for (int i=1; i<=n; i++)
26             for (int j=1; j<=n; j++)
27             {
28                 if (node[i][j]>node[i][k]+node[k][j])
29                     node[i][j]=node[i][k]+node[k][j];
30             }
31     }
32     return Min;
33 }
34 
35 int main ()
36 {
37     int m;
38     while (~scanf("%d%d",&n,&m))
39     {
40         for (int i=1; i<=n; i++)
41         {
42             for (int j=1; j<=n; j++)
43                 map[i][j]=node[i][j]=INF;
44         }
45         while (m--)
46         {
47             int a,b,c;
48             scanf("%d%d%d",&a,&b,&c);
49             if (map[a][b]>c)
50                 map[a][b]=map[b][a]=c;
51         }
52         floyd();
53         if (Min==INF)
54             printf ("It‘s impossible.\n");
55         else
56             printf ("%d\n",Min);
57     }
58     return 0;
59 }