#include <bits/stdc++.h>
#define task "M"
#define all(v) (v).begin(), (v).end()
#define rep(i, l, r) for (int i = (l); i <= (r); ++i)
#define Rep(i, r, l) for (int i = (r); i >= (l); --i)
#define DB(X) { cerr << #X << " = " << (X) << '\n'; }
#define DB1(A, _) { cerr << #A << "[" << _ << "] = " << (A[_]) << '\n'; }
#define DB2(A, _, __) { cerr << #A << "[" << _ << "][" << __ << "] = " << (A[_][__]) << '\n'; }
#define DB3(A, _, __, ___) { cerr << #A << "[" << _ << "][" << __ << "][" << ___ << "] = " << (A[_][__][___]) << '\n'; }
#define PR(A, l, r) { cerr << '\n'; rep(_, l, r) DB1(A, _); cerr << '\n';}
#define SZ(x) ((int)(x).size())
#define pb push_back
#define eb emplace_back
#define pf push_front
#define F first
#define S second
#define by(x) [](const auto& a, const auto& b) { return a.x < b.x; } // sort(arr, arr + N, by(a));
#define next ___next
#define prev ___prev
#define y1 ___y1
#define left ___left
#define right ___right
#define y0 ___y0
#define div ___div
#define j0 ___j0
#define jn ___jn
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using namespace std;
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vl;
int read(){int s=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){s=(s<<3)+(s<<1)+ch-'0',ch=getchar();}return s*f;}
const int N = 1e4 + 1, INF = 1e9;
int n, K, r, dp[N][N][2], sz[N], f[2][2][N];
vii g[N];
void upd(int &x, int y) {x = min(x, y);}
void dfs(int u, int p)
{
for (ii v : g[u]) if (v.F != p)
{
dfs(v.F, u);
sz[u] += sz[v.F];
}
sz[u]++;
int now = 0, lst = 1, szz = 1;
rep(i, 0, 1) rep(j, 0, min(K, sz[u])) dp[u][j][i] = f[now][i][j] = INF;
f[0][0][1] = f[0][1][1] = 0;
for (ii v : g[u]) if (v.F != p)
{
szz += sz[v.F];
now ^= 1, lst ^= 1;
rep(i, 0, 1) rep(j, 0, min(K, sz[u])) f[now][i][j] = f[lst][i][j];
rep(k, 2, min(K, szz)) rep(k1, 1, min(k - 1, sz[v.F]))
{
upd(f[now][0][k], f[lst][0][k - k1] + dp[v.F][k1][1] + 2 * v.S);
upd(f[now][1][k], f[lst][1][k - k1] + dp[v.F][k1][1] + 2 * v.S);
upd(f[now][1][k], f[lst][0][k - k1] + dp[v.F][k1][0] + v.S);
}
}
rep(k, 1, min(K, sz[u]))
{
dp[u][k][0] = f[now][1][k], dp[u][k][1] = f[now][0][k];
}
}
int main()
{
#ifdef HynDuf
freopen(task".in", "r", stdin);
//freopen(task".out", "w", stdout);
#else
ios_base::sync_with_stdio(false); cin.tie(nullptr);
#endif
n = read(), K = read(), r = read();
rep(i, 2, n)
{
int u, v, w;
//cin >> u >> v >> w;
u = read();
v = read();
w = read();
g[u].eb(v, w);
g[v].eb(u, w);
}
dfs(r, 0);
printf("%d", dp[r][K][0]);
return 0;
}
