#include <bits/stdc++.h>
using namespace std;
// * No One Dies a Virgin, Life Fucks Us All
typedef long long ll;
#define nl '\n'
#define ff first
#define ss second
#define pb push_back
#define sik(x) {cout << x << nl; return;}
constexpr ll maxn = 1e4+4, mod = 1e9 + 7, inf = 2e14, SQ = 450, LG = 20;
typedef pair<int, int> pii;
int n, K, X, sz[maxn];
vector<pii> g[maxn];
inline void mins(ll& a, ll b) { a = min(a, b); }
void dfs(int v, int p, vector<ll>& dp, vector<ll>& pd) {
sz[v] = 1;
dp.assign(sz[v] + 1, 0);
pd.assign(sz[v] + 1, 0);
for (auto [u, w] : g[v]) {
if (u == p) continue;
vector<ll> dpu, pdu;
dfs(u, v, dpu, pdu);
vector<ll> tmp1, tmp2;
tmp1.assign(min<int>(K + 1, dp.size() + dpu.size() + 1), inf);
tmp2.assign(min<int>(K + 1, pd.size() + pdu.size() + 1), inf);
for (int i = 0 ; i <= min(sz[v], K) ; i ++) {
mins(tmp1[i], dp[i]);
mins(tmp2[i], pd[i]);
for (int j = 1 ; j <= min(sz[u], K) ; j ++) {
if (i + j <= K) {
mins(tmp1[i + j], dp[i] + dpu[j] + 2 * w);
mins(tmp2[i + j], dp[i] + pdu[j] + w);
mins(tmp2[i + j], dpu[j] + 2 * w + pd[i]);
}
}
}
sz[v] += sz[u];
dp.swap(tmp1);
pd.swap(tmp2);
dp.resize(K + 1);
pd.resize(K + 1);
}
}
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> K >> X;
for (int i = 1 , u, v, w ; i < n ; i ++) {
cin >> u >> v >> w;
g[u].pb({v, w});
g[v].pb({u, w});
}
vector<ll> dp, pd;
dfs(X, 0, dp, pd);
cout << pd[K] << nl;
}
