#include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <vector>

 #include <algorithm>

 using namespace std;

 const int maxn =  + ;

 int n, s;

 vector<int> G[maxn], C[maxn];

 int len, id;

 void dfs(int u, int fa, int d)

 {

     if(d > len) { len = d; id = u; }

     for(int i = ; i < G[u].size(); i++)

     {

         int v = G[u][i];

         if(v == fa) continue;

         dfs(v, u, d + C[u][i]);

     }

 }

 int main()

 {

     while(scanf("%d%d", &n, &s) == )

     {

         for(int i = ; i <= n; i++) { G[i].clear(); C[i].clear(); }

         int sum = ;

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

         {

             int u, v, d; scanf("%d%d%d", &u, &v, &d);

             sum += d * ;

             G[u].push_back(v); C[u].push_back(d);

             G[v].push_back(u); C[v].push_back(d);

         }

         int a;

         len = -;

         dfs(, , );

         len = -;

         a = id;

         dfs(a, , );

         printf("%d\n", sum - len);

     }

     return ;

 }