#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<bool> vb;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,k,n) for(ll i=(ll)(k);i<(ll)(n);i++)
#define all(a) a.begin(),a.end()
#define fi first
#define se second
#define pb emplace_back
#define lb(v,k) (lower_bound(all(v),k)-v.begin())
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outp(T p){cout<<'('<<p.fi<<','<<p.se<<')'<<endl;}
template<class T> void ouvp(T v){for(auto p:v)cout<<'('<<p.fi<<','<<p.se<<')';cout<<endl;}
template<class T> void outvv(T v){for(auto x:v)outv(x);}
const ll inf=1001001001001001001;
int main(){
ll n,k,s;cin>>n>>k>>s;s--;
vvp g(n);
rep(i,n-1){
ll a,b,c;cin>>a>>b>>c;
a--;b--;
g[a].pb(b,c);
g[b].pb(a,c);
}
vvi dp0(n),dp1(n);
vi dep(n);
function<void(ll,ll)> dfs=[&](ll i,ll p){
dp0[i].pb(0);dp1[i].pb(-dep[i]);
for(auto x:g[i])if(x.fi!=p){
dep[x.fi]=dep[i]+x.se;
dfs(x.fi,i);
rep(j,dp0[x.fi].size()){
dp0[i].pb(inf);dp1[i].pb(inf);
}
for(int j=dp0[i].size()-1;j>=0;j--)if(dp0[i][j]!=inf){
rep(k,dp0[x.fi].size()){
chmin(dp0[i][j+k+1],dp0[i][j]+dp0[x.fi][k]+x.se*2);
chmin(dp1[i][j+k+1],dp0[i][j]+dp1[x.fi][k]+x.se*2);
chmin(dp1[i][j+k+1],dp1[i][j]+dp0[x.fi][k]+x.se*2);
}
}
}
};dfs(s,-1);
out(dp1[s][k-1]);
}
