//Oh? You're Approaching Me?
#include <bits/stdc++.h>
using namespace std;
//
#define int long long
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
// #pragma GCC optimize("O3,unroll-loops")
#define migmig ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define pb push_back
#define F first
#define S second
#define SZ(x) ll((x).size())
#define all(x) (x).begin(), (x).end()
#define cl clear
#define endl '\n'
#define deb(x) cerr << #x << " = " << x << '\n'
#define dokme(x) {cout << x << endl; return;}
#define wtf cout << "[ahaaaaaaaaaaaaaaaa]" << endl;
const int maxn = 1e4 + 10;
const int mod = 1e9 + 7;
const int inf = 1e18 + 5;
const int LOG = 21;
const int sq = 320;
// #define mid ((l + r) / 2)
// #define lc (id * 2)
// #define rc (lc + 1)
//g++ main.cpp -o main && main.exe
int n, k, x, dp[maxn][maxn], pd[maxn][maxn], sz[maxn];
vector<pii> G[maxn];
void dfs(int v, int p) {
dp[v][1] = pd[v][1] = 0;
sz[v] = 1;
for (auto [u, w]: G[v]) {
if (u == p)
continue;
dfs(u, v);
for (int x = sz[v]; x >= 1; x--) {
for (int y = sz[u]; y >= 1; y--) {
pd[v][x + y] = min(pd[v][x + y], pd[v][x] + pd[u][y] + 2 * w);
dp[v][x + y] = min(dp[v][x + y], pd[v][x] + dp[u][y] + w);
dp[v][x + y] = min(dp[v][x + y], dp[v][x] + pd[u][y] + 2 * w);
}
}
sz[v] += sz[u];
}
}
signed main() {
migmig;
cin >> n >> k >> x;
for (int i = 1; i < n; i++) {
int v, u, w;
cin >> v >> u >> w;
G[v].pb({u, w});
G[u].pb({v, w});
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
dp[i][j] = pd[i][j] = inf;
}
}
dfs(x, 0);
// cout << pd[x][k] << '\n';
cout << min(pd[x][k], dp[x][k]) << '\n';
}
