#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
// typedefs...
typedef double db;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<ll, ll> pll;
typedef trie<string,null_type,trie_string_access_traits<>,pat_trie_tag,trie_prefix_search_node_update>pref_trie;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> oset;
// constants...
const double PI = acos(-1);
const ll mod = 1e9 + 7; // 998244353
const int MXS = 2e5+5;
const ll MXI = 1e9+5;
const ll MXL = 1e18+5;
const ll INF = 1e9+5;
const ll INFLL = 1e18+5;
const ll EPS = 1e-9;
// defines...
#define MP make_pair
#define PB push_back
#define fi first
#define se second
#define ordered_set tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>
#define boost_ ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0);
#define endl '\n'
// functions...
ll gcd(ll a, ll b){ while (b){ a %= b; swap(a, b);} return a;}
ll lcm(ll a, ll b){ return (a/gcd(a, b)*b);}
ll ncr(ll a, ll b){ ll x = max(a-b, b), ans=1; for(ll K=a, L=1; K>=x+1; K--, L++){ ans = ans * K; ans /= L;} return ans;}
ll bigmod(ll a,ll b,ll mod){ if(b==0){ return 1;} ll tm=bigmod(a,b/2,mod); tm=(tm*tm)%mod; if(b%2==1) tm=(tm*a)%mod; return tm;}
ll egcd(ll a,ll b,ll &x,ll &y){ if(a==0){ x=0; y=1; return b;} ll x1,y1; ll d=egcd(b%a,a,x1,y1); x=y1-(b/a)*x1; y=x1; return d;}
ll modpow(ll a,ll p,ll mod) {ll ans=1;while(p){if(p%2)ans=(ans*a)%mod;a=(a*a)%mod;p/=2;} return ans;}
ll inverse_mod(ll n,ll mod) {return modpow(n,mod-2,mod);}
vector<pii> v[10005];
vector<int> dp[10001][2];
int n, k, st;
int check(int pos, int pre, int rd) {
dp[pos][0].PB(0);
dp[pos][1].PB(0);
int sz = 0;
for(auto it : v[pos]) {
if(it.fi == pre) continue;
sz += check(it.fi, pos, it.se);
}
for(int i = 1; i <= min(sz, k - 1); i++) {
dp[pos][0].PB(INF);
dp[pos][1].PB(INF);
}
for(auto it : v[pos]) {
if(it.fi == pre) continue;
// cout << pos << "--" << it.fi << endl;
for(int i = min(sz, k - 1); i >= 1; i--) {
// overall i + 1 nodes
for(int j = 0; j < dp[it.fi][0].size(); j++) {
// taking j + 1 nodes
if(j + 1 > i) continue;
// cout << i << j + 1 << endl;
// cout << i - j - 1 << endl;
dp[pos][0][i] = min(dp[pos][0][i], dp[it.fi][0][j] + dp[pos][0][i - j - 1] + 2 * it.se);
dp[pos][1][i] = min(dp[pos][1][i], dp[it.fi][1][j] + dp[pos][0][i - j - 1] + it.se);
}
}
}
return sz + 1;
}
void solve() {
cin >> n >> k >> st;
for(int i = 1; i < n; i++) {
int x, y, c;
cin >> x >> y >> c;
v[x].PB({y, c});
v[y].PB({x, c});
}
check(st, st, 0);
cout << dp[st][1][k-1] << endl;
}
int main()
{
boost_;
int t=1;
// cin>>t;
for(int i=1;i<=t;i++)
{
// cout<<"Case "<<i<<": ";
solve();
}
}
/*
1 3
0 2
*/
