#include <bits/stdc++.h>
using namespace std;
vector < pair <int , int> > adiacenta[10001];
vector <int> minim[10001][2];
int dorit;
inline void Parcurgere (const int nod , const int adancime , const int sursa)
{
minim[nod][0].resize(2);
minim[nod][1].resize(2);
for (auto vecin : adiacenta[nod]) {
if (vecin.first != sursa)
{
Parcurgere(vecin.first , adancime + 1 , nod);
if ((int)minim[nod][0].size() < dorit - adancime + 1)
{ minim[nod][0].resize(min(dorit - adancime + 1 , (int)minim[nod][0].size() + (int)minim[vecin.first][0].size() - 1) , 1000000000); }
if ((int)minim[nod][1].size() < dorit - adancime + 1)
{ minim[nod][1].resize(min(dorit - adancime + 1 , (int)minim[nod][1].size() + (int)minim[vecin.first][1].size() - 1) , 1000000000); }
for (int total = (int)minim[nod][1].size() - 1 ; total > 1 ; total--) {
for (int termen = min(total - 1 , (int)minim[vecin.first][1].size() - 1) ; termen ; termen--)
{ minim[nod][1][total] = min({minim[nod][1][total] , minim[nod][1][total - termen] + minim[vecin.first][0][termen] + 2 * vecin.second , minim[nod][0][total - termen] + minim[vecin.first][1][termen] + vecin.second}); }
}
for (int total = (int)minim[nod][0].size() - 1 ; total > 1 ; total--) {
for (int termen = min(total - 1 , (int)minim[vecin.first][0].size() - 1) ; termen ; termen--)
{ minim[nod][0][total] = min(minim[nod][0][total] , minim[nod][0][total - termen] + minim[vecin.first][0][termen] + 2 * vecin.second); }
}
}
}
}
int main ()
{
ios :: sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int numar_noduri , inceput;
cin >> numar_noduri >> dorit >> inceput;
for (int indice = 1 ; indice < numar_noduri ; indice++)
{
int nod[2] , cost;
cin >> nod[0] >> nod[1] >> cost;
adiacenta[nod[0]].push_back({nod[1] , cost});
adiacenta[nod[1]].push_back({nod[0] , cost});
}
Parcurgere(inceput , 0 , 0);
cout << minim[inceput][1][dorit];
return 0;
}
