#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn=1e4+10;
int sz[maxn];
int dp[2][maxn][maxn];
vector<pair<int,int>>g[maxn];
int n,k,x,a,b,c;
void dfs(int node,int par)
{
dp[1][node][1]=dp[0][node][1]=0;
sz[node]=1;
for(auto ax:g[node])
{
if(ax.first==par)continue;
dfs(ax.first,node);
for(int i=min(k,sz[node]+sz[ax.first]);i>=2;i--)
{
for(int j=min(i-1,sz[ax.first]);j>=max(1LL,i-sz[node]);j--)
{
dp[1][node][i]=min({dp[1][node][i],dp[0][node][i-j]+dp[1][ax.first][j]+ax.second,dp[1][node][i-j]+dp[0][ax.first][j]+2*ax.second});
dp[0][node][i]=min(dp[0][node][i],dp[0][node][i-j]+dp[0][ax.first][j]+2*ax.second);
}
}
sz[node]+=sz[ax.first];
}
}
signed main()
{
cin>>n>>k>>x;
for(int i=0;i<n-1;i++)
{
cin>>a>>b>>c;
g[a].push_back({b,c});
g[b].push_back({a,c});
}
for(int i=0;i<maxn;i++)
{
for(int j=0;j<maxn;j++)
{
dp[0][i][j]=dp[1][i][j]=1e9;
}
}
dfs(x,-1);
cout<<dp[1][x][k]<<endl;
return 0;
}
