#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define TranLeThanhTam "TranLeThanhTam"
#define all(v) v.begin(),v.end()
#define reset(a,i) memset(a,i,sizeof(a))
#define FOR(i,a,b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i,a,b) for (int i = (a), _b = (b); i >= _b; --i)
#define compact(v) sort(all(v)), v.erase(unique(all(v)), end(v))
#define sz(v) (int) v.size()
#define MASK(i) (1 << (i))
typedef long long ll;
typedef long double lb;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
const int Thanh_Tam = 2 * 1e5 + 17;
const int inf = 1e9 + 17;
const long long infll = 1e18 + 17;
const int MOD = 1e9 + 7;
const int Log = 18;
const int dx[4] = {-1, 0, 0, 1};
const int dy[4] = {0, -1, 1, 0};
const int max_block_size = 600;
const ll P = 311;
const int maxA = 1e2 + 17;
const int addi = 1e9;
const char dir[4] = {'W', 'S', 'N', 'E'};
const int Mod[3] = {998244353, MOD, 759186269};
ll mul(ll a, ll b, ll mod);
ll binpow(ll a, ll b, ll mod)
{
ll res = 1;
while (b > 0)
{
if (b & 1) res = mul(res,a,mod);
b >>= 1;
a = mul(a,a,mod);
}
return res;
}
ll add(ll a, ll b, ll mod = MOD) { return (a + b) % mod; }
ll sub(ll a, ll b, ll mod = MOD) { return (a - b + mod) % mod; }
ll mul(ll a, ll b, ll mod = MOD) { return ((a % mod) * (b % mod)) % mod; }
ll Div(ll a, ll b, ll mod = MOD) { return mul(a, binpow(b, mod - 2, mod), mod); }
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rand_range(ll l, ll r) { return uniform_int_distribution<ll>(l,r)(rng); }
int n, k, root, ans = 0;
vector<pii> adj[Thanh_Tam];
int h[Thanh_Tam], child[Thanh_Tam], is_part_of_tree[Thanh_Tam], par[Thanh_Tam];
priority_queue<pii> pq;
void dfs(int u)
{
is_part_of_tree[u] = true;
for (pii T : adj[u])
{
int v = T.fi, w = T.se;
if (v == par[u]) continue;
par[v] = u;
++child[u];
h[v] = h[u] + w;
dfs(v);
}
if (child[u] == 0) pq.push({h[u] - h[par[u]], u});
return;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
if (fopen(TranLeThanhTam".inp","r"))
{
freopen(TranLeThanhTam".inp","r",stdin);
freopen(TranLeThanhTam".out","w",stdout);
}
cin >> n >> k >> root;
FOR(i, 2, n)
{
int u, v, w;
cin >> u >> v >> w;
adj[u].pb({v, w});
adj[v].pb({u, w});
ans += w;
}
ans <<= 1;
dfs(root);
while (n > k)
{
int val = pq.top().fi, v = pq.top().se;
pq.pop();
ans -= val << 1;
--child[par[v]];
if (child[par[v]] == 0 && par[v] != root)
pq.push({h[par[v]] - h[par[par[v]]], par[v]});
--n;
}
int tmp = 0;
while (!pq.empty())
{
tmp = max(tmp, h[pq.top().se]);
pq.pop();
}
cout << ans - tmp;
return 0;
}
