#include<bits/stdc++.h>
using namespace std;
#define ll int
#define fi first
#define se second
#define p(x,y) pair<ll,ll>(x,y)
#define BIT(i,x) ((x>>i)&1)
#define MASK(x) (1<<x)
#define ld long double
#define __builtin_popcount __builtin_popcountll
#define pll pair<ll,ll>
template<class T1,class T2>
bool maximize(T1 &x,const T2 &y)
{
if(x<y)
{
x=y;
return 1;
}
return 0;
}
template<class T1,class T2>
bool minimize(T1 &x,const T2 &y)
{
if(x>y)
{
x=y;
return 1;
}
return 0;
}
void online()
{
std::ios_base::sync_with_stdio(0);
cin.tie(0);
#ifndef ONLINE_JUDGE
// freopen("input.inp", "r", stdin);
// freopen("output.out","w", stdout);
#else
#endif
}
const ll N=1e4+10,M=5e8+7;
vector<ll> f[N][2];
ll f1[2][N],tt,n,x,c[N],par[N],cost[N];
vector<pll> gr[N];
void dfs(ll u)
{
ll h=0;
c[u]=1;
for(auto [v,w]:gr[u])
{
if(v==par[u]) continue;
par[v]=u;
cost[v]=w;
dfs(v);
c[u]+=c[v];
if(c[v]>c[h]) h=v;
}
f[u][0].resize(min(c[u],tt)+2,M);
f[u][1].resize(min(c[u],tt)+2,M);
f[u][0][1]=f[u][1][1]=0;
ll cr=1;
if(h)
{
for(int i=1;i<=min(c[h],tt);i++)
{
minimize(f[u][0][i+1],f[h][0][i]+2*cost[h]);
minimize(f[u][1][i+1],f[h][1][i]+cost[h]);
}
cr+=c[h];
}
for(auto [v,w]:gr[u])
{
if(v==h||v==par[u]) continue;
cr+=c[v];
minimize(cr,tt);
for(int k=0;k<=cr;k++) f1[0][k]=f[u][0][k],f1[1][k]=f[u][1][k];
for(int k=2;k<=cr;k++)
{
for(int j=1;j<=min(k-1,c[v]);j++)
{
minimize(f1[0][k],f[u][0][k-j]+f[v][0][j]+2*w);
minimize(f1[1][k],f[u][1][k-j]+f[v][0][j]+2*w);
minimize(f1[1][k],f[u][0][k-j]+f[v][1][j]+w);
}
}
for(int k=0;k<=cr;k++) f[u][0][k]=f1[0][k],f[u][1][k]=f1[1][k];
}
}
int main()
{
online();
cin>>n>>tt>>x;
for(int i=1;i<n;i++)
{
ll u,v,w;
cin>>u>>v>>w;
gr[u].emplace_back(v,w);
gr[v].emplace_back(u,w);
}
dfs(x);
cout<<f[x][1][tt];
}
