#include<bits/stdc++.h>
#define fo(i,d,c) for(int i=d;i<=c;i++)
#define fod(i,c,d) for(int i=c;i>=d;i--)
#define maxn 1000010
#define N 1010
#define fi first
#define se second
#define pb emplace_back
#define en cout<<"\n";
#define int long long
#define inf 1000000000
#define pii pair<int,int>
#define vii vector<pii>
#define lb(x) x&-x
#define bit(i,j) ((i>>j)&1)
#define offbit(i,j) (i^(1<<j))
#define onbit(i,j) (i|(1<<j))
#define vi vector<int>
template <typename T1, typename T2> bool minimize(T1 &a, T2 b){if (a > b) {a = b; return true;} return false;}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b){if (a < b) {a = b; return true;} return false;}
using namespace std;
int n,k,x;
vii ke[maxn];
int f[10001][10001][2];
int sz[maxn];
void dfs(int u,int parent)
{
sz[u] = 1;
for(auto [v,w] : ke[u])
{
if(v == parent) continue;
dfs(v,u);
sz[u] += sz[v];
fod(i,sz[u],2) fo(j,max(0LL,i - sz[u] + sz[v]),min(i,sz[v]))
{
f[u][i][0] = min(f[u][i][0],f[v][j][1] + f[u][i - j][0] + 2 * w);
f[u][i][0] = min(f[u][i][0],f[v][j][0] + f[u][i - j][1] + w);
f[u][i][1] = min(f[u][i][1],f[v][j][1] + f[u][i - j][1] + 2 * w);
}
}
}
main()
{
#define name "TASK"
if(fopen(name".inp","r"))
{
freopen(name".inp","r",stdin);
freopen(name".out","w",stdout);
}
ios_base::sync_with_stdio(false);cin.tie(NULL);
cin >> n >> k >> x;
fo(i,1,n - 1)
{
int u,v,w;
cin >> u >> v >> w;
ke[u].pb(v,w);
ke[v].pb(u,w);
}
fo(i,1,n) fo(j,2,k) f[i][j][0] = f[i][j][1] = inf;
dfs(x,x);
cout << f[x][k][0];
}
