#include <iostream>
// #include <fstream>
// std::ifstream cin ("boarding.in");
// std::ofstream cout ("boarding.out");
#include <cmath>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <vector>
#include <array>
#include <algorithm>
#include <numeric>
#include <iomanip>
#include <unordered_set>
#include <stack>
#include <tuple>
#include <ext/pb_ds/assoc_container.hpp>
#include <random>
#include <chrono>
#include <bitset>
#include <complex>
#include <tuple>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
template <typename T, typename U>
bool emin(T &a, const U &b) { return b < a ? a = b, true : false; }
template <typename T, typename U>
bool emax(T &a, const U &b) { return b > a ? a = b, true : false; }
template <class T> using iset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef uint64_t hash_t;
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
const ll M = (1LL << 61) - 1;
const ll B = uniform_int_distribution<ll>(0, M - 1)(rng);
__int128 mul(ll a, ll b) { return (__int128)a * b; }
__int128 add(ll a, ll b) { return (__int128)a + b; }
ll mod_mul(ll a, ll b) { return mul(a, b) % M; }
ll mod_add(ll a, ll b) { return add(a, b) % M; }
const ll inf = (ll) 1e18;
int n, k, s;
vector<vector<pair<ll, ll>>> a;
vector<vector<vector<ll>>> dp;
vector<ll> comp(vector<ll> a, vector<ll> b, ll x) {
vector<ll> c(a.size() + b.size() - 1, inf);
for(int i = 0; i < a.size(); i++) {
for(int j = 0; j < b.size(); j++) {
emin(c[i + j], a[i] + b[j] + (i || j ? x : 0));
}
}
for(int i = 0; i < a.size(); i++) emin(c[i], a[i]);
for(int i = 0; i < b.size(); i++) emin(c[i], b[i]);
return c;
}
void go(int x, int y = -1) {
dp[0][x] = {0, 0};
dp[1][x] = {0, 0};
for(auto &u : a[x]) {
if(u.first == y) continue;
go(u.first, x);
dp[1][x] = comp(dp[1][x], dp[0][u.first], u.second * 2);
auto temp = comp(dp[0][x], dp[1][u.first], u.second);
for(int i = 0; i < dp[1][x].size(); i++) emin(dp[1][x][i], temp[i]);
dp[0][x] = comp(dp[0][x], dp[0][u.first], u.second * 2);
}
}
int main() {
cin >> n >> k >> s; s--;
a = vector<vector<pair<ll, ll>>>(n);
dp = vector<vector<vector<ll>>>(2, vector<vector<ll>>(n));
for(int i = 0; i < n - 1; i++) {
ll x, y, z;
cin >> x >> y >> z;
x--, y--;
a[x].push_back({y, z}), a[y].push_back({x, z});
}
go(s);
cout << dp[1][s][k];
}
