#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;
#define MAXN 10000
#define INF 1000000000
struct Edge
{
int a, b, c;
int other(int node) {
return (node == a) ? b : a;
}
};
int n, k, x, i, sz[MAXN+2];
int dpcyc[MAXN+2][MAXN+2], dp[MAXN+2][MAXN+2];
vector<int> nb[MAXN+2];
Edge edges[MAXN+2];
void dfs1(int node)
{
sz[node] = 1;
dpcyc[node][1] = dp[node][1] = 0;
for (auto e : nb[node]) {
int x = edges[e].other(node);
int c = edges[e].c;
if (!sz[x]) {
dfs1(x);
for (int i = sz[node]+1; i <= sz[node]+sz[x]; i++) {
dpcyc[node][i] = dp[node][i] = INF;
}
for (int i = sz[node]; i >= 1; i--) {
for (int j = sz[x]; j >= 1; j--) {
dpcyc[node][i+j] = min(dpcyc[node][i+j], dpcyc[node][i] + dpcyc[x][j] + 2*c);
dp[node][i+j] = min(dp[node][i+j], dp[node][i] + dpcyc[x][j] + 2*c);
dp[node][i+j] = min(dp[node][i+j], dpcyc[node][i] + dp[x][j] + c);
}
}
sz[node] += sz[x];
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> k >> x;
for (i = 1; i < n; i++) {
cin >> edges[i].a >> edges[i].b >> edges[i].c;
nb[edges[i].a].push_back(i);
nb[edges[i].b].push_back(i);
}
dfs1(x);
cout << dp[x][k];
return 0;
}
