#include <bits/stdc++.h>
#define Pc_champs ios_base::sync_with_stdio(false);cout.tie(NULL);cin.tie(NULL);
#define int long long
#define ll long long
using namespace std;
int const N = 1e4 + 1, LOG = 18, N2 = 1e5 + 1, SQ = 710, M = 1e9 + 7;
int const MX = (int) 1e12;
vector<vector<pair<int, int>>> adj;
vector<int> dp[2][N];
vector<int> val;
vector<int> mrg(vector<int> a, vector<int> b) {
vector<int> combine(a.size() + b.size() - 1, MX);
for (int i = 0; i < a.size(); ++i) {
for (int j = 0; j < b.size(); ++j) {
combine[i + j] = min(combine[i + j], a[i] + b[j]);
}
}
return combine;
}
void dfs(int u, int v = 0) {
dp[0][u] = {0};
dp[1][u] = {0};
for (auto i: adj[u]) {
if (i.first == v)continue;
val[i.first] = i.second;
dfs(i.first, u);
vector<int> cur = mrg(dp[1][u], dp[0][i.first]);
dp[1][u] = mrg(dp[0][u], dp[1][i.first]);
for (int j = 0; j < cur.size(); ++j) dp[1][u][j] = min(dp[1][u][j], cur[j]);
dp[0][u] = mrg(dp[0][u], dp[0][i.first]);
}
dp[0][u].emplace_back();
dp[1][u].emplace_back();
for (int i = dp[0][u].size() - 1; i; --i) {
dp[0][u][i] = dp[0][u][i - 1] + 2 * val[u];
dp[1][u][i] = dp[1][u][i - 1] + val[u];
}
}
int n, k, x, idx;
void dowork() {
cin >> n >> k >> x;
adj = vector<vector<pair<int, int>>>(n + 1);
val = vector<int>(n + 1);
for (int i = 0, u, v, c; i < n - 1; ++i) {
cin >> u >> v >> c;
adj[u].emplace_back(v, c);
adj[v].emplace_back(u, c);
}
dfs(x);
cout << dp[1][x][k];
}
signed main() {
Pc_champs
int t = 1;
//cin >> t;
while (t--) {
++idx;
dowork();
cout << '\n';
}
}
