#include<bits/stdc++.h>
using namespace std;
const int maxn = 10004;
int n, k, x;
int f[maxn][maxn], g[maxn][maxn], sub[maxn];
vector<pair<int,int>> adj[maxn];
inline void MIN(int &x, int y)
{
x = min(x, y);
}
void merge(int x, int y, int w)
{
for (int i = sub[x]; i >= 0; i--)
for (int j = sub[y]; j >= 0; j--)
{
MIN(f[x][i + j], min(f[x][i] + g[y][j] + w * 2, g[x][i] + f[y][j] + w));
MIN(g[x][i + j], g[x][i] + g[y][j] + w * 2);
}
sub[x] += sub[y];
}
void dfs(int x, int p = 0)
{
f[x][1] = g[x][1] = 0;
sub[x] = 1;
for (auto [i, j] : adj[x]) if (i != p)
{
dfs(i, x);
merge(x, i, j);
}
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
// freopen("test.inp", "r", stdin);
// freopen("test.out", "w", stdout);
cin >> n >> k >> x;
for (int i = 1, u, v, w; i < n; i++)
cin >> u >> v >> w,
adj[u].emplace_back(v, w),
adj[v].emplace_back(u, w);
memset(f, 0x3f, sizeof f);
memset(g, 0x3f, sizeof g);
dfs(x);
cout << min(f[x][k], g[x][k]);
}
