#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
// #ifndef ONLINE_JUDGE
// #include "00_debug.h"
// #else
// #define debug(x)
// #endif
#define endl '\n'
#define all(a) a.begin(), a.end()
typedef long long ll;
using namespace std;
using namespace __gnu_pbds;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T> using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
void solve(){
int n,k,x;
cin>>n>>k>>x;
vector<vector<pair<int,int>>>g(n);
for(int i=1;i<n;i++){
int u,v,w;
cin>>u>>v>>w;
u--,v--;
g[u].push_back({v,w});
g[v].push_back({u,w});
}
vector<vector<vector<int>>>dp(n);
vector<int>sz(n);
vector<int>mx(n);
function<void(int,int)>dfs1=[&](int node,int parent){
mx[node]=1;
for(auto child:g[node]){
if(child.first==parent)continue;
dfs1(child.first,node);
mx[node]+=mx[child.first];
}
};
x--;
dfs1(x,-1);
function<void(int,int)>dfs=[&](int node,int parent){
for(auto child:g[node]){
if(child.first==parent)continue;
dfs(child.first,node);
}
dp[node]=vector<vector<int>>(mx[node]+1,vector<int>(2,1e9));
dp[node][1][1]=0;
dp[node][1][0]=0;
sz[node]=1;
for(auto child:g[node]){
if(child.first==parent)continue;
auto ndp=dp[node];
for(int i=0;i<=min(sz[node],k);i++){
if(dp[node][i][1]==1e9)continue;
for(int j=0;j<=min(sz[child.first],k)&&j+i<=k;j++){
if(dp[child.first][j][0]!=1e9){
ndp[i+j][0]=min(ndp[i+j][0],dp[node][i][1]+dp[child.first][j][0]+child.second);
}
if(dp[child.first][j][1]!=1e9){
ndp[i+j][1]=min(ndp[i+j][1],dp[node][i][1]+dp[child.first][j][1]+2*child.second);
ndp[i+j][0]=min(ndp[i+j][0],dp[node][i][1]+dp[child.first][j][1]+child.second);
ndp[i+j][0]=min(ndp[i+j][0],dp[node][i][0]+dp[child.first][j][1]+2*child.second);
}
}
}
sz[node]+=sz[child.first];
swap(ndp,dp[node]);
}
};
dfs(x,-1);
cout<<dp[x][k][0]<<endl;
}
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// #ifndef ONLINE_JUDGE
// freopen("Input.txt","r",stdin);
// freopen("output.txt","w",stdout);
// freopen("Error.txt","w",stderr);
// #endif
int t=1;
// cin >> t;
while(t--){
solve();
}
return 0;
}
