#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pli pair<ll, ll>
#define RUN_LIKE_DJAWAD (ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0));
#define DECIMAL_OUTPUT cout << fixed << setprecision(9);
#define pb push_back
#define pf push_top
#define ff first
#define ss second
#define maxn 10001
#define inf 200000000
vector<pii> g[maxn];
int E1[maxn], E2[maxn], H1[maxn], H2[maxn];
bool seen[maxn];
int dfs(int v, int pt){
seen[v] = true;
E1[pt] = 0, E2[pt] = 0;
int SZN = 1;
for (auto [u, w]: g[v]) if (not seen[u]){
int szc = dfs(u, pt + SZN);
for (int i = 0; i < SZN; i++) H1[i] = E1[pt + i], H2[i] = E2[pt + i];
for (int i = 0; i < szc; i++) H1[SZN + i] = inf, H2[SZN + i] = inf;
for (int i = 0; i < SZN; i++) for (int j = 0; j < szc; j++){
H1[i + j + 1] = min({H1[i + j + 1], E1[pt + i] + E2[pt + SZN + j] + (w << 1), E2[pt + i] + E1[pt + SZN + j] + w});
H2[i + j + 1] = min(H2[i + j + 1], E2[pt + i] + E2[pt + SZN + j] + (w << 1));
}
SZN += szc;
for (int i = 0; i < SZN; i++) E1[pt + i] = H1[i], E2[pt + i] = H2[i];
}
return SZN;
}
int n, k, s, ui, vi, ci;
int main(){
RUN_LIKE_DJAWAD
cin >> n >> k >> s;
for (int i = 1; i < n; i++){
cin >> ui >> vi >> ci;
g[ui].pb({vi, ci});
g[vi].pb({ui, ci});
}
dfs(s, 0);
cout << E1[k - 1] << "\n";
}
