#include <bits/stdc++.h>
#define int long long
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define F first
#define S second
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()
#define kill(x) cout << x << "\n", exit(0);
#define pii pair<int, int>
#define endl "\n"
using namespace std;
typedef long long ll;
// typedef __int128_t lll;
typedef long double ld;
const int MAXN = (int)1e4 + 7;
const int MOD = 998244353;
const ll INF = (ll)1e18 + 7;
const int LG = 20;
int n, m, k, tmp, t, tmp2, tmp3, tmp4, u, v, w, flag, q, ans, flag2;
int arr[MAXN], arr2[MAXN], sz[MAXN];
vector<pii> adj[MAXN];
vector<int> dp[2][MAXN];
void DFS(int v, int p=0) {
dp[0][v] = {0, 0}; dp[1][v] = {0, 0}; sz[v] = 1;
for (auto cur:adj[v]) {
int u = cur.F, w = cur.S;
if (u == p) continue;
DFS(u, v);
vector<int> pd[2];
pd[0].resize(sz[v]+sz[u]+1); fill(all(pd[0]), INF);
pd[1].resize(sz[v]+sz[u]+1); fill(all(pd[1]), INF);
for (int x=0; x<=sz[v]; x++) {
for (int y=0; y<=sz[u]; y++) {
pd[1][x+y] = min(pd[1][x+y], dp[1][v][x]+dp[1][u][y]+2*w);
pd[0][x+y] = min(pd[0][x+y], dp[1][v][x]+dp[0][u][y]+w);
pd[0][x+y] = min(pd[0][x+y], dp[0][v][x]+dp[1][u][y]+2*w);
if (!y) pd[1][x] = min(pd[1][x], dp[1][v][x]);
if (!y) pd[0][x] = min(pd[0][x], dp[0][v][x]);
}
}
dp[0][v] = pd[0]; dp[1][v] = pd[1]; sz[v] += sz[u];
}
}
int32_t main() {
#ifdef LOCAL
freopen("inp.in", "r", stdin);
freopen("res.out", "w", stdout);
#else
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#endif
cin >> n >> k >> m;
for (int i=1; i<n; i++) {
cin >> u >> v >> w;
adj[u].pb({v, w}); adj[v].pb({u, w});
}
DFS(m);
cout << dp[0][m][k] << endl;
return 0;
}
