//KZNS
#include <cstdio>
#include <vector>
#include <utility>
#include <cstring>
using namespace std;
#define Nmax 50004
#define Kmax 23
typedef pair<int, int> pr;
vector<pr> gp[Nmax];
int N, R, K;
void init() {
    scanf("%d %d %d", &N, &R, &K);
    int a, b, c; 
    for (int i = 1; i < N; i++) {
        scanf("%d %d %d", &a, &b, &c);
        gp[a].push_back(make_pair(b, c));
        gp[b].push_back(make_pair(a, c)); 
    }
}
int fa[Nmax];
void DFS(int x, int *F) {
    int v;
    int mn;
    int G[Kmax];
    for (int i = 0; i < gp[x].size(); i++) {
        if (fa[x] == gp[x][i].first)
            continue;
        memset(G, 0, sizeof(G));
        fa[gp[x][i].first] = x;
        DFS(gp[x][i].first, G);
        v = gp[x][i].second;
        for (int k = K; k >= 0; k--) {
            mn = F[k] + G[0] + v*2;
            for (int g = 1; g <= k; g++)
                mn = min(mn, F[k-g] + G[g] + g * v);
            F[k] = mn;
        }
        //for (int k = 1; k <= K; k++)
        //    F[k] = min(F[k], F[k-1]);
    }
}
int main() {
    freopen("trobot.in", "r", stdin);
    freopen("trobot.out", "w", stdout);
    init();
    int F[Kmax] = {0};
    DFS(R, F);
    printf("%d\n", F[K]);
    return 0;
}
//UBWH