#include <bits/stdc++.h>
#define int long long
using namespace std;
const int MAXN = 500000 + 5;
int n, s;
struct Edge
{
    int v, w;
};
vector<Edge> e[MAXN];
int dp[MAXN], len[MAXN];
void dfs(int u, int fa)
{
    int maxLen = 0;
    dp[u] = 0;
    for (int i = 0; i < e[u].size(); i++)
    {
        int v = e[u][i].v;
        int w = e[u][i].w;
        if (v == fa)
            continue;
        dfs(v, u);
        maxLen = max(maxLen, w + len[v]);
        dp[u] += dp[v];
    }
    len[u] = maxLen;
    for (int i = 0; i < e[u].size(); i++)
    {
        int v = e[u][i].v;
        int w = e[u][i].w;
        if (v == fa)
            continue;
        dp[u] += maxLen - (w + len[v]);
    }
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> s;
    for (int i = 1; i <= n - 1; i++)
    {
        int u, v, w;
        cin >> u >> v >> w;
        e[u].push_back((Edge){v, w});
        e[v].push_back((Edge){u, w});
    }
    dfs(s, 0);
    cout << dp[s];
    return 0;
}