#include <bits/stdc++.h>
#define ll long long
#define int long long
#define F first
#define S second
#define MAXN 10005
#define ii pair<int,int>
#define bit(i,j) ((i>>j)&1)
#define sz(i) (int)i.size()
#define endl '\n'
using namespace std;
const int INF = 1e18;
int n, k, st;
vector<ii>g[MAXN];
namespace sub1
{
vector<int> dp[MAXN][2];
vector<int> combine(vector<int>x, vector<int>y, int w)
{
vector<int>ans(sz(x) + sz(y) - 1, INF);
for(int i = 1; i < sz(x); i++)
for(int j = 0; j < sz(y); j++)
if(i + j <= k)
ans[i + j] = min(ans[i + j], x[i] + y[j] + w);
return ans;
}
vector<int>mn(vector<int>x, vector<int>y)
{
for(int i = 0; i < sz(x); i++)
y[i] = min(x[i], y[i]);
return y;
}
void dfs(int u, int p, int cost)
{
dp[u][0] = {0, cost};
dp[u][1] = {INF, cost};
for(ii i : g[u])
{
int v = i.F, w = i.S;
if(v == p)
continue;
dfs(v, u, w);
dp[u][1] = mn(dp[u][1], combine(dp[u][1], dp[v][0], w));
dp[u][1] = mn(dp[u][1], combine(dp[u][0], dp[v][1], 0));
dp[u][0] = mn(dp[u][0], combine(dp[u][0], dp[v][0], w));
}
}
void solve()
{
dfs(st, 0, 0);
cout << dp[st][1][k];
}
}
main()
{
if(fopen("TEST.inp","r"))
{
freopen("TEST.inp","r",stdin);
freopen("TEST.out","w",stdout);
}
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k >> st;
for(int i = 1; i < n; i++)
{
int x, y, z;
cin >> x >> y >> z;
g[x].push_back({y, z});
g[y].push_back({x, z});
}
sub1::solve();
}
