#include <bits/stdc++.h>
using namespace std;
#define INPFILE ".inp"
#define OUTFILE ".out"
const int INF = 3e8 + 7;
template <class T1, class T2>
inline bool minimise(T1 &x, T2 y) {
if (x > y) { x = y; return true; }
return false;
}
template <class T>
inline void minimise_pair(pair<T, T> &x, T y) {
if (x.second > y)
swap(x.second, y);
if (x.first > x.second)
swap(x.second, x.first);
}
const int MAX = 1e4 + 3;
int N, K, ROOT;
vector<pair<int, int>> adj[MAX];
void input() {
cin >> N >> K >> ROOT;
for (int t = N - 1; t--; ) {
int u, v, w; cin >> u >> v >> w;
adj[u].emplace_back(v, w);
adj[v].emplace_back(u, w);
}
}
int dp[2][MAX][MAX], sz[MAX];
void dfs(int u, int p) {
sz[u] = 1;
for (const auto &e : adj[u]) {
int v, w;
tie(v, w) = e;
if (v == p) continue;
dfs(v, u);
sz[u] += sz[v];
}
static int g[MAX][2];
g[0][true ] = 0;
g[0][false] = 0;
for (int s = min(K, sz[u]); s >= 1; s--)
g[s][true ] = g[s][false] = INF;
int cum_size = 1;
for (const auto &e : adj[u]) {
int v, w;
tie(v, w) = e;
if (v == p) continue;
for (int s = min(K, cum_size + sz[v]); s >= 1; s--) {
for (int y = min(s, sz[v] + 1); y >= 1; y--) {
int x = s - y;
minimise(g[s][true ], g[x][true ] + 2 * w + dp[true ][v][y - 1]);
minimise(g[s][false], g[x][false] + 2 * w + dp[true ][v][y - 1]);
minimise(g[s][false], g[x][true ] + w + dp[false][v][y - 1]);
if (x > cum_size)
break;
}
}
cum_size += sz[v];
}
dp[true ][u][0] = 0;
dp[false][u][0] = 0;
for (int k = 1; k <= min(K, sz[u]); k++) {
minimise(dp[false][u][k], g[k][false]);
minimise(dp[true ][u][k], g[k][true ]);
}
}
void solve() {
if (K == 1) {
cout << 0;
return;
}
for (int t : {0, 1})
for (int u = 0; u <= N; u++)
for (int k = 0; k <= K; k++)
dp[t][u][k] = INF;
adj[0].emplace_back(ROOT, 0);
dfs(0, -1);
int ans = dp[false][0][K];
cout << ans;
}
int main(void) {
if (fopen(INPFILE, "r")) {
freopen(INPFILE, "r", stdin);
freopen(OUTFILE, "w", stdout);
}
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
input();
solve();
return 0;
}
