#include <bits/stdc++.h>
using namespace std;
#define zedanov \
ios_base::sync_with_stdio(0); \
cin.tie(0); \
cout.tie(0);
#define el "\n"
const int N = 1e4 + 1, md = 1e9 + 7, inf = 1e9;
// Verify Logic, Check Constrains
// Overflow, Fits in Time/Memory ?
vector<pair<int, int>> a[N];
int sub[N], dp[N][N][2], temp[N][2];
void dfs(int node, int par)
{
sub[node] = 1;
dp[node][0][0] = dp[node][0][1] = 0;
dp[node][1][0] = dp[node][1][1] = 0;
for (auto& [ch, w] : a[node])
{
if (ch == par)
continue;
dfs(ch, node);
for (int i = 0; i <= sub[node] + sub[ch]; i++)
{
temp[i][0] = inf;
temp[i][1] = inf;
}
for (int i = 0; i <= sub[node]; i++)
{
temp[i][0] = dp[node][i][0];
temp[i][1] = dp[node][i][1];
}
for (int x = 1; x <= sub[node]; x++)
{
for (int y = 1; y <= sub[ch]; y++)
{
// don't end at node's subtree
temp[x + y][0] = min(temp[x + y][0], dp[node][x][0] + dp[ch][y][0] + 2 * w);
// end at nodes' subtree but not in child's
temp[x + y][1] = min(temp[x + y][1], dp[node][x][1] + dp[ch][y][0] + 2 * w);
// end at child's subtree
temp[x + y][1] = min(temp[x + y][1], dp[node][x][0] + dp[ch][y][1] + w);
}
}
sub[node] += sub[ch];
for (int i = 0; i <= sub[node]; i++)
{
dp[node][i][0] = temp[i][0];
dp[node][i][1] = temp[i][1];
}
}
}
void doWork()
{
int n, k, x;
cin >> n >> k >> x;
for (int i = 0; i < n - 1; i++)
{
int u, v, w;
cin >> u >> v >> w;
a[u].emplace_back(v, w);
a[v].emplace_back(u, w);
}
for (int i = 0; i <= n; i++)
{
for (int j = 0; j <= n; j++)
dp[i][j][0] = dp[i][j][1] = inf;
}
dfs(x, 0);
cout << min(dp[x][k][0], dp[x][k][1]);
}
signed main()
{
zedanov int t = 1;
// cin >> t;
while (t--)
doWork();
return 0;
}
