#include <algorithm>

#include <cstdio>

#include <cstring>

#include <string>

#include <cmath>

#include <iostream>

#include <map>

#include <queue>

#include <set>

#include <vector>

using namespace std;

#define max3(x, y, z) max(max((x), (y)), (z))

#define min3(x, y, z) min(mix((x), (y)), (z))

#define pb push_back

#define ppb pop_back

#define mk make_pair

#define pii pair<int, int>

#define pll pair<long long, long long>

#define debug_l(a) cout << #a << " " << (a) << endl

#define debug_b(a) cout << #a << " " << (a) << " "

#define testin(filename) freopen((filename) ,"r",stdin)

#define testout(filename) freopen((filename) ,"w",stdout)

typedef long long ll;

typedef unsigned long long ull;

const double PI  = 3.14159265358979323846264338327;

const double E   = exp();

const double eps = 1e-;

const int INF    = 0x3f3f3f3f;

const int NINF   = 0xc0c0c0c0;

using namespace std;

const int MAXN = ;

struct edge

{

    int from, to, cost;

    edge(int f, int t, int c) : from(f), to(t), cost(c) {}

};

int d[MAXN];

bool vis[MAXN];

vector<edge>edges;

vector<int>G[MAXN];

typedef pair<int, int> P;

void Dijkstra(int s) {

    priority_queue<P, vector<P>, greater<P> > que;

    fill(d, d + MAXN, INF);

    fill(vis, vis + MAXN, );

    d[s] = ;

    que.push(make_pair(, s));

    while (!que.empty()) {

        P p = que.top(); que.pop();

        int v = p.second;

        if (d[v] < p.first) continue;        //d[v] < p.first 说明，v 点已经通过其他路径变得松弛，距离更短。而 p.first 只是之前入队的旧元素

        for (int i = ; i < G[v].size(); i++) {

            edge e = edges[G[v][i]];

            if (d[e.to] > d[v] + e.cost) {

                d[e.to] = d[v] + e.cost;

                que.push(P(d[e.to], e.to));

            }

        }

    }

}

int main() {

    //testin("data.in");

    int n, p, k;

    scanf("%d%d%d", &n, &p, &k);

    for (int i = ; i < n - ; i++) {

        int f, t, c;

        scanf("%d%d%d", &f, &t, &c);

        edges.push_back(edge(f, t, c));

        G[f].push_back(edges.size() - );

        edges.push_back(edge(t, f, c));

        G[t].push_back(edges.size() - );

    }

    Dijkstra(p);

    sort(d, d + n + );

    printf("%d\n", d[k]);

    return ;

}