#include <bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define sp << " " <<
using namespace std;
const int N = 5001,MOD = 998244353,inf = 1e18;
vi cnt(N,0),sz(N,0);
vector<pii> edges[N];
vi dp[N],dp2[N];
void dfs(int node,int p) {
sz[node] = 1;
dp[node] = {inf,0};
dp2[node] = {inf,0};
for (auto it : edges[node]) {
if (it.ff == p) continue;
dfs(it.ff,node);
while (dp[node].size() < sz[node]+sz[it.ff]+1) dp[node].push_back(inf);
while (dp2[node].size() < sz[node]+sz[it.ff]+1) dp2[node].push_back(inf);
vi dpp = dp[node],dppp = dp2[node];
for (int j = 1;j<=sz[node];j++) {
for (int k = 1;k<=sz[it.ff];k++) {
dp2[node][j+k] = min(dp2[node][j+k],dppp[j]+dp2[it.ff][k]+2*it.ss);
dp[node][j+k] = min(dp[node][j+k],dpp[j]+dp2[it.ff][k]+2*it.ss);
dp[node][j+k] = min(dp[node][j+k],dppp[j]+dp[it.ff][k]+it.ss);
}
}
sz[node]+=sz[it.ff];
}
}
void solve() {
int n,k,x;
cin >> n >> k >> x;
for (int i=1;i<=n-1;i++) {
int a,b,c;
cin >> a >> b >> c;
edges[a].push_back({b,c});
edges[b].push_back({a,c});
}
dfs(x,x);
cout << dp[x][k] << '\n';
}
signed main() {
ios_base::sync_with_stdio(0);cin.tie(0);
#ifdef Dodi
freopen("in.txt","r",stdin);
freopen("out.txt","w",stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
