#include <bits/stdc++.h>
#define el '\n'
#define FNAME "MUSEUM"
#define allof(x) x.begin(),x.end()
#define allof1(x) x.begin()+1,x.end()
#define mset(x,n) memset(x,(n),sizeof(x))
using namespace std;
const long long MOD = (long long) 1e9+7;
template<class X,class Y> bool minimize(X &a,Y b){ if (a>b) {a=b; return true;} return false;}
template<class X,class Y> bool maximize(X &a,Y b){ if (a<b) {a=b; return true;} return false;}
void setup(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
if (fopen(FNAME".inp","r")){
freopen(FNAME".inp","r",stdin);
freopen(FNAME".out","w",stdout);
}
}
const int MAXN = 1e4 + 1;
struct Edges{
int v,w;
Edges(): v(0),w(0) {}
Edges(int V,int W):v(V),w(W) {}
bool operator < (const Edges &other) const{
return w>other.w;
}
};
int n,K,S;
vector<Edges> graph[MAXN];
void init(){
cin>>n>>K>>S;
for (int i=1;i<n;i++){
int u,v,w;
cin>>u>>v>>w;
graph[u].emplace_back(v,w);
graph[v].emplace_back(u,w);
}
}
int sz[MAXN];
/*
* dp[u][k][*]: minimum time to visit K nodes in U'S subtree
* 0 = starting and ending at U
* 1 = starting at U and ending at anywhere
*/
int dp[MAXN][MAXN][2];
void dfs(int u,int pre){
sz[u] = 1;
dp[u][1][0] = dp[u][1][1] = 0;
for (Edges x : graph[u]){
int v = x.v;
int w = x.w;
if (v==pre) continue;
dfs(v,u);
for (int i = min(K,sz[u]); i>=1;i--){
for (int j = min(K-i,sz[v]); j>=1; j--){
minimize(dp[u][i+j][0], dp[u][i][0] + dp[v][j][0] + 2 * w );
int sumFree = min(dp[u][i][0] + dp[v][j][1] + w,
dp[u][i][1] + dp[v][j][0] + 2 * w );
minimize(dp[u][i+j][1], sumFree);
}
}
sz[u] += sz[v];
}
}
void sol(){
mset(dp,0x3f3f3f3f);
dfs(S,S);
cout<<min(dp[S][K][0],dp[S][K][1]);
}
int main(){
setup();
init();
sol();
}
