/*
Author: Nguyen Chi Thanh - High School for the Gifted - VNU.HCM (i2528)
*/
#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1ll << (x)))
#define debug(a, l, r) for (int _i = (l); _i <= (r); ++_i) cout << (a)[_i] << ' '; cout << '\n';
const int MAXN = 1e4 + 5;
const int INF = 2e9 + 7;
int n, k, x;
vector<pii> adj[MAXN];
int dp[2][MAXN][MAXN], sz[MAXN];
int g[2][MAXN];
void init() {
cin >> n >> k >> x;
for (int i = 1; i < n; ++i) {
int u, v, w; cin >> u >> v >> w;
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
}
void minimize(int &x, int y) {
x = min(x, y);
}
void dfs(int u, int par = -1) {
sz[u] = 1;
for (auto &e : adj[u]) {
int v = e.fi;
if (v == par) continue;
dfs(v, u);
sz[u] += sz[v];
}
for (int i = 0; i <= sz[u]; ++i) {
g[0][i] = INF;
g[1][i] = INF;
}
g[0][0] = 0; g[1][0] = 0;
int cursz = 0;
for (auto &e : adj[u]) {
int v = e.fi, w = e.se;
if (v == par) continue;
for (int i = cursz; i >= 0; --i)
for (int j = 1; j <= sz[v]; ++j) {
minimize(g[0][i + j], g[0][i] + dp[0][v][j] + 2 * w);
minimize(g[1][i + j], g[1][i] + dp[0][v][j] + 2 * w);
minimize(g[1][i + j], g[0][i] + dp[1][v][j] + w);
}
cursz += sz[v];
}
for (int i = 1; i <= sz[u]; ++i) {
dp[0][u][i] = g[0][i - 1];
dp[1][u][i] = g[1][i - 1];
}
}
void solve() {
dfs(x);
cout << dp[1][x][k];
}
signed main() {
#ifdef NCTHANH
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
init();
solve();
return 0;
}
