1 #include "bits/stdc++.h"
 2 #define mem(a,b) memset(a,b,sizeof(a))
 3 using namespace std;
 4 typedef long long LL;
 5 const int MAX=105;
 6 const int oo=100000000;
 7 int ans;
 8 int n,m;
 9 int dist[MAX][MAX],a[MAX][MAX];
10 inline int mn(int x,int y){return x<y?x:y;}
11 void floyd(){
12     ans=oo;
13     int i,j,k;
14     for (k=1;k<=n;k++){
15         for (i=1;i<k;i++){
16             for (j=i+1;j<k;j++){
17                 ans=mn(ans,a[i][k]+a[k][j]+dist[i][j]);
18             }
19         }
20         for (i=1;i<=n;i++){
21             for (j=1;j<=n;j++){
22                 dist[i][j]=mn(dist[i][j],dist[i][k]+dist[k][j]);
23             }
24         }
25     }
26 }
27 int main(){
28     freopen ("find.in","r",stdin);
29     freopen ("find.out","w",stdout);
30     int i,j;
31     int u,v,w;
32     while (~scanf("%d%d",&n,&m)){
33         for (i=1;i<=n;i++) for (j=1;j<=n;j++) dist[i][j]=a[i][j]=(i==j?0:oo);
34         for (i=1;i<=m;i++){
35             scanf("%d%d%d",&u,&v,&w);
36             if (w<a[u][v]) 
37              a[u][v]=a[v][u]=dist[u][v]=dist[v][u]=w;
38         }
39         floyd();
40         if (ans>=oo)
41          puts("It‘s impossible.");
42         else printf("%d\n",ans);
43     }
44     return 0;
45 }