#include <bits/stdc++.h>
using namespace std;
#define MOD1 1000000007
#define MOD2 998244353
#define fir first
#define sec second
#define pushf push_front
#define pushb push_back
#define popf pop_front
#define popb pop_back
#define mp make_pair
#define all(a) a.begin(), a.end()
#define lbound(v, x) lower_bound(all(v), x) - v.begin()
#define ubound(v, x) upper_bound(all(v), x) - v.begin()
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define FOR1(a) for (int _ = 0; _ < (a); ++_)
#define FOR2(i, a) for (int i = 0; i < (a); ++i)
#define FOR3(i, a, b) for (int i = (a); i < (b); ++i)
#define RFOR1(a) for (int _ = (a)-1; _ >= 0; --_)
#define RFOR2(i, a) for (int i = (a)-1; i >= 0; --i)
#define RFOR3(i, a, b) for (int i = (b)-1; i >= (a); --i)
#define overload3(a, b, c, d, ...) d
#define REP(...) overload3(__VA_ARGS__, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define RREP(...) overload3(__VA_ARGS__, RFOR3, RFOR2, RFOR1)(__VA_ARGS__)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<vb> vvb;
typedef vector<vc> vvc;
typedef vector<vpii> vvpii;
typedef vector<vpll> vvpll;
typedef queue<int> qi;
typedef queue<ll> qll;
typedef queue<pii> qpii;
typedef queue<pll> qpll;
typedef deque<int> dqi;
typedef deque<ll> dqll;
typedef deque<pii> dqpii;
typedef deque<pll> dqpll;
typedef priority_queue<int> pqi;
typedef priority_queue<ll> pqll;
typedef priority_queue<pii> pqpii;
typedef priority_queue<pll> pqpll;
typedef priority_queue<int, vi, greater<int> > r_pqi;
typedef priority_queue<ll, vll, greater<ll> > r_pqll;
typedef priority_queue<pii, vpii, greater<pii> > r_pqpii;
typedef priority_queue<pll, vpll, greater<pll> > r_pqpll;
const ll inf = 1e16;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n;
int k, r;
cin>>n>>k>>r;
vvpii adj(n);
REP(i, n-1) {
int a, b, c;
cin>>a>>b>>c;
adj[a-1].pushb(mp(b-1, c));
adj[b-1].pushb(mp(a-1, c));
}
vvpll dp(n, vpll(n+1, mp(inf, inf)));
function<int(int, int)> dfs = [&](int u, int p) {
int sz = 1;
dp[u][0] = mp(0, 0);
dp[u][1] = mp(0, 0);
for(auto [v, w] : adj[u]) {
if(v == p) {
continue;
}
// cerr<<u<<' '<<v<<endl;
int t = dfs(v, u);
RREP(i, 1, min(k, sz)+1) {
RREP(j, 1, min(k-i, t)+1) {
chmin(dp[u][i+j].fir, dp[u][i].sec + dp[v][j].fir + w);
chmin(dp[u][i+j].fir, dp[u][i].fir + dp[v][j].sec + w*2);
chmin(dp[u][i+j].sec, dp[u][i].sec + dp[v][j].sec + w*2);
}
}
sz += t;
}
// cerr<<u<<' '<<sz<<endl;
return sz;
};
dfs(r-1, -1);
// REP(i, n) {
// REP(j, n+1) {
// cerr<<(dp[i][j].fir == inf ? -1 : dp[i][j].fir)<<' '<<(dp[i][j].sec == inf ? -1 : dp[i][j].sec)<<"; ";
// }
// cerr<<endl;
// }
cout<<dp[r-1][k].fir;
}
