#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
using namespace std;
using ll = long long;
using ull = unsigned long long;
using db = double;
constexpr int inf = 1e9 + 7;
constexpr ll INF = 1e18 + 14;
constexpr int mod = 1e9 + 7;
constexpr int maxn = 3e5 + 100;
constexpr int maxm = 2e6 + 100;
constexpr db eps = 1e-6;
ll inv2, inv3;
inline char get(void) {
static char buf[1 << 19], *p1 = buf, *p2 = buf;
if (p1 == p2) {
p2 = (p1 = buf) + fread(buf, 1, 1 << 19, stdin);
if (p1 == p2) return EOF;
}
return *p1++;
}
template<typename T>
inline void read(T &x) {
x = 0; static char c; bool minus = false;
for (; !(c >= '0' && c <= '9'); c = get()) if (c == '-') minus = true;
for (; c >= '0' && c <= '9'; x = x * 10 + c - '0', c = get()); if (minus) x = -x;
}
template<typename T>
void add(T& x, const T& y) {if((x += y) >= mod) x -= mod;}
template<typename T>
void dec(T& x, const T& y) {if((x -= y) < 0) x += mod;}
template<typename T>
void cmax(T& x, const T& y) {if(y > x) x = y;}
template<typename T>
void cmin(T& x, const T& y) {if(y < x) x = y;}
ll qpow(ll x, ll a){
ll base = x, rt = 1;
while(a){
if(a & 1) rt *= base, rt %= mod;
base *= base, base %= mod;
a >>= 1;
}
return rt;
}
ll inv(ll a){
if(a < 0) a += mod;
return qpow(a, mod - 2);
}
int lowbit(int x){
return x & (-x);
}
ll lcm(ll a, ll b){
ll g = __gcd(a, b);
return a / g * b;
}
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
vector<ll> fac, ifac;
void init_fac(){
fac.resize(maxn), ifac.resize(maxn);
fac[0] = fac[1] = 1;
for(int i = 2; i < maxn; i++) fac[i] = fac[i - 1] * i % mod;
ifac[maxn - 1] = inv(fac[maxn - 1]);
for(int i = maxn - 2; i >= 0; i--) ifac[i] = ifac[i + 1] * (i + 1) % mod;
}
ll C(int n, int m){
return fac[n] * ifac[m] % mod * ifac[n - m] % mod;
}
vector<int> prime, np, divi;
void init_prime(){
np.resize(maxm); divi.resize(maxm);
for(int i = 2; i < maxm; i++){
if(!np[i]) {prime.push_back(i); divi[i] = i;}
for(auto v: prime){
if(v * i >= maxm) break;
np[v * i] = 1; divi[v * i] = v;
if(i % v == 0) break;
}
}
}
void init(){
}
void solve() {
int n, k, rt; cin >> n >> k >> rt;
vector e(n + 1, vector(0, pair(0, 0)));
for (int i = 1; i < n; i++) {
int u, v, w; cin >> u >> v >> w;
e[u].emplace_back(v, w); e[v].emplace_back(u, w);
}
vector dp(n + 1, vector(k + 1, array<int, 2>{inf, inf}));
auto dfs = [&](auto&& self, int u, int fa) -> int {
int siz = 1;
dp[u][1] = {0, 0};
for (auto [v, w]: e[u]) {
if (v == fa) continue;
auto csiz = self(self, v, u);
for (int i = min(siz + csiz, k); i > 0; i--) for (int j = min(csiz, i); j >= max(1, i - siz); j--) {
// cerr << dp[u][i][0] << endl;
cmin(dp[u][i][0], dp[u][i - j][0] + dp[v][j][0] + 2 * w);
cmin(dp[u][i][1], dp[u][i - j][0] + dp[v][j][1] + w);
cmin(dp[u][i][1], dp[u][i - j][1] + dp[v][j][0] + 2 * w);
// cerr << i << ' ' << dp[u][i][0] << ' ' << dp[u][i][1] << endl;
// cerr << i << ' ' << j << ' ' << dp[u][i - j][0] << ' ' << dp[v][j][0] << endl;
}
siz += csiz;
}
return siz;
};
dfs(dfs, rt, 0);
cout << dp[rt][k][1] << endl;
}
int main(){
// cerr << inv(2) << endl;
// clock_t st = clock(), ed;
#ifndef ONLINE_JUDGE
freopen("1.in", "r", stdin);
freopen("my.out", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(nullptr);
// srand(114514);
init();
int t = 1;
cout << setprecision(3) << fixed;
cerr << setprecision(2) << fixed;
// cin >> t;
// read(t);
while(t--){
solve();
}
// ed = clock();
// double endtime=(double)(ed-st)/CLOCKS_PER_SEC;
// cout<<"Total time:"<<endtime<<endl;
// system("pause");
return 0;
}
