#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define gcd __gcd
#define sz(v) (int) v.size()
#define pb push_back
#define pi pair<int,int>
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())
#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define dbg(x) "[" #x " = " << (x) << "]"
///#define int long long
using ll = long long;
using ld = long double;
using ull = unsigned long long;
template<typename T> bool ckmx(T& a, const T& b){if(a < b) return a = b, true; return false;}
template<typename T> bool ckmn(T& a, const T& b){if(a > b) return a = b, true; return false;}
const int N = 2e5+5;
const ll MOD = 1e9+7;
const ll INF = 1e18;
void solve()
{
int n,k,start; cin >> n >> k >> start;
vector<vector<pair<int,int>>> adj(n+1, vector<pair<int,int>>());
FOR(i, 1, n-1){
int u,v,c; cin >> u >> v >> c;
adj[u].emplace_back(v, c);
adj[v].emplace_back(u, c);
}
vector<int> sz; sz.resize(n+1);
vector<vector<vector<ll>>> dp(n+1, vector<vector<ll>>(2, vector<ll>()));
function<vector<vector<ll>>(vector<vector<ll>>&, vector<vector<ll>>&)> combine = [&](vector<vector<ll>>& dad, vector<vector<ll>>& child){
vector<vector<ll>> combined(2, vector<ll>(sz(dad[0]) + sz(child[0]) - 1, INF));
FOR(i, 0, sz(dad[0]) - 1){
combined[0][i] = dad[0][i];
combined[1][i] = dad[1][i];
}
FOR(i, 1, sz(child[0]) - 1){
combined[0][i] = min(combined[0][i], child[0][i]);
combined[1][i] = min(combined[1][i], child[1][i]);
}
FOR(i, 1, sz(dad[0]) - 1){
FOR(j, 1, sz(child[0]) - 1){
combined[0][i + j] = min(combined[0][i + j], dad[0][i] + child[0][j]);
combined[1][i + j] = min(combined[1][i + j], dad[0][i] + child[1][j]);
combined[1][i + j] = min(combined[1][i + j], dad[1][i] + child[0][j]);
}
}
return combined;
};
auto dfs = [&](auto&& dfs, int x, int p) -> void{
dp[x][0] = {(ll)1e12, (ll)0};
dp[x][1] = {(ll)1e12, (ll)0};
sz[x] = 1;
for(pair<int,int> e : adj[x]){
int v = e.first, w = e.second;
if(v != p){
dfs(dfs, v, x);
FOR(i, 1, sz[v]){
dp[v][0][i] = dp[v][0][i] + 2ll * w;
dp[v][1][i] = dp[v][1][i] + 1ll * w;
}
sz[x] += sz[v];
dp[x] = combine(dp[x], dp[v]);
}
}
};
dfs(dfs, start, - 1);
cout << min(dp[start][1][k], dp[start][0][k]) <<"\n";
return;
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#define name "InvMOD"
if(fopen(name".INP", "r")){
freopen(name".INP","r",stdin);
freopen(name".OUT","w",stdout);
}
int t = 1; //cin >> t;
while(t--) solve();
return 0;
}
