#include <bits/stdc++.h>
#define pii pair<int,int>
#define f first
#define s second
using namespace std;
const int mn = 1e4+1, INF=1e9;
int dp[2][mn][mn],sub[mn],k;
vector<pii> edges[mn];
void dfs(int c, int p)
{
sub[c]=1;
dp[0][c][1]=0;
for (pii i : edges[c])
if (i.f!=p)
{
dfs(i.f,c);
sub[c]+=sub[i.f];
for (int j=sub[c];j>1;++j)
for (int K=1;K<=sub[i.f];++K)
{
dp[0][c][j]=min(dp[0][c][j],dp[0][c][j-K]+dp[0][i.f][K]+2*i.s);
dp[1][c][j]=min(dp[1][c][j],dp[0][c][j-K]+dp[1][i.f][K]);
}
}
//cout<<c<<" "<<sub[c]<<"\n";
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
int n,x,a,b,c;
cin>>n>>k>>x;
for (int i=1;i<n;++i)
{
cin>>a>>b>>c;
edges[a].push_back({b,c});
edges[b].push_back({a,c});
}
for (int i=1;i<=n;++i)
for (int j=1;j<=k;++j)
{
dp[0][i][j]=INF;
dp[1][i][j]=INF;
}
dfs(x,0);
cout<<dp[1][x][k];
return 0;
}
