#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define sz(x) (int)x.size()
#define ALL(v) v.begin(),v.end()
#define MASK(k) (1LL << (k))
#define BIT(x, i) (((x) >> (i)) & 1)
#define oo (ll)1e18
#define INF (ll)1e9
#define MOD (ll)(1e9 + 7)
using namespace std;
template<class T1, class T2>
bool maximize(T1 &a, T2 b){if(a < b){a = b; return true;} return false;}
template<class T1, class T2>
bool minimize(T1 &a, T2 b){if(a > b){a = b; return true;} return false;}
template<class T1, class T2>
void add(T1 &a, T2 b){a += b; if(a >= MOD) a -= MOD;}
template<class T1, class T2>
void sub(T1 &a, T2 b){a -= b; if(a < 0) a += MOD;}
template<class T>
void cps(T &v){sort(ALL(v)); v.resize(unique(ALL(v)) - v.begin());}
const int MAX = 1e4 + 10;
int N, K, S;
vector<pair<int, int>> adj[MAX];
vector<ll> dp[MAX][2];
int cnt[MAX];
void dfs(int u, int p = -1){
cnt[u] = 1;
for(auto o: adj[u]){
int v = o.fi;
if(v == p) continue;
dfs(v, u);
cnt[u] += cnt[v];
}
for(int i = 0; i < 2; i++){
dp[u][i].resize(cnt[u] + 3, oo);
}
dp[u][1][1] = dp[u][0][1] = 0;
int cur = 1;
for(auto o: adj[u]){
int v = o.fi;
int c = o.se;
if(v == p) continue;
for(int i = cur; i >= 1; i--){
for(int j = cnt[v]; j >= 1; j--){
minimize(dp[u][0][i + j], dp[u][0][i] + dp[v][0][j] + 2 * c);
minimize(dp[u][1][i + j], dp[u][1][i] + dp[v][0][j] + 2 * c);
minimize(dp[u][1][i + j], dp[u][0][i] + dp[v][1][j] + c);
}
}
cur += cnt[v];
for(int i = 0; i < 2; i++){
dp[v][i].clear();
}
}
}
void solve(){
cin >> N >> K >> S;
for(int i = 1; i < N; i++){
int u, v, c; cin >> u >> v >> c;
adj[u].push_back({v, c});
adj[v].push_back({u, c});
}
dfs(S);
cout << dp[S][1][K] << '\n';
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
// freopen("btower.inp","r",stdin);
// freopen("btower.out","w",stdout);
int t = 1;
// cin >> t;
while(t--){
solve();
}
return 0;
}
