#include<bits/stdc++.h>
#define fi first
#define se second
#define ll long long
using namespace std;
const int N=1e4,INF=1e8+9;
int n,dp[N+5][N+5],f[N+5];
int bd[N+5],nex[N+5],par[N+5],cnt=0,ke[N+5];
vector<pair<int,int>> g[N+5];
void dfs(int u,int pa){
cnt++;bd[cnt]=u;
for (auto j:g[u]){
if (j.fi==pa) continue;
if (ke[u]==0) ke[u]=j.fi;
par[j.fi]=u;f[j.fi]=f[u]+j.se;
dfs(j.fi,u);
}
nex[u]=cnt+1;
}
int get(int u,int v,int pa){
return f[u]+f[v]-2*f[pa];
}
int ff(int u,int k){
if (k<0) return INF;
if (u>n){
if (k==0) return 0;return INF;
}
if (dp[u][k]!=INF) return dp[u][k];
int ans=INF;
if (ke[u]!=0) ans=min(ans,ff(ke[u],k-1)+get(u,ke[u],u));
int z=bd[nex[u]];
if (z<=n){
ans=min(ans,ff(z,k)+get(par[u],z,par[z])-get(u,par[u],par[u]));
ans=min(ans,ff(z,k-1)+get(u,z,par[z]));
}
else ans=min(ans,ff(z,k));
// cout<<u<<" "<<k<<" "<<ke[u]<<" "<<ans<<endl;
return dp[u][k]=ans;
}
int main(){
if (fopen("museum.inp","r")){
freopen("museum.inp","r",stdin);
freopen("museum.out","w",stdout);
}
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin>>n;
int k,x;cin>>k>>x;
for (int i=1;i<n;i++){
int u,v,w;cin>>u>>v>>w;
g[u].push_back({v,w});
g[v].push_back({u,w});
}
bd[n+1]=n+1;
dfs(x,x);
for (int i=1;i<=n;i++){
for (int j=0;j<=k;j++) dp[i][j]=INF;
}
// cout<<get()<<endl;
cout<<ff(x,k-1);
}
