#include <iostream>

 #include <cstdio>

 #include <algorithm>

 #include <cstring>

 using namespace std;

 const int INF = 0x3f3f3f3f;

 const int Max =  + ;

 int g[Max][Max], dist[Max][Max];

 //dist【i】【j】保存i到j的最短路经，然后i -> j -> k 就可以枚举k， dist[i][j] + g[i][k] + g[j][k]就是一个环的权值

 int mincost;

 void Floyed(int n)

 {

     mincost = INF;

     for (int k = ; k <= n; k++)

     {

         for (int i = ; i < k; i++)

         {

             for (int j = i + ; j < k; j++)

             {

                 if (dist[i][j] != INF && g[i][k] != INF && g[k][j] != INF)

                 {

                     int temp = dist[i][j] + g[i][k] + g[k][j]; // 原先这里直接相加，一直没找到错误，爆精度

                     if (temp < mincost)

                         mincost = temp;

                 }

             }

         }

         for (int i = ; i <= n; i++)

         {

             for (int j = ; j <= n; j++)

             {

                 if (dist[i][k] != INF && dist[k][j] != INF)

                     dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);

             }

         }

     }

 }

 int main()

 {

     int n, m;

     while (scanf("%d%d", &n, &m) != EOF)

     {

         for (int i = ; i < Max; i++)

             for (int j = ; j < Max; j++)

             {

                 g[i][j] = INF;

                 dist[i][j] = INF;

             }

         int a, b, c;

         for (int i = ; i <= m; i++)

         {

             scanf("%d%d%d", &a, &b, &c);

             if (g[a][b] > c)

                 g[a][b] = g[b][a] = dist[a][b] = dist[b][a] = c;

         }

         Floyed(n);

         if (mincost >= INF)

             printf("It's impossible.\n");

         else

             printf("%d\n", mincost);

     }

     return ;

 }