#include <cstdio>

#include <algorithm>

#define maxn 500010

int head[maxn], cnt;

struct Edge {

	int to, nxt, w;

} e[maxn << 1];

inline void add(int a, int b, int c) {

	e[++cnt] = (Edge) {b, head[a], c}; head[a] = cnt;

}

long long ans[maxn], M[maxn];

void dfs(int u, int fa = 0) {

	for (int i = head[u]; i; i = e[i].nxt) {

		int v = e[i].to;

		if (v != fa) {

			dfs(v, u);

			M[u] = std::max(M[u], M[v] + e[i].w);

			ans[u] += ans[v];

		}

	}

	for (int i = head[u]; i; i = e[i].nxt) {

		int v = e[i].to;

		if (v != fa) ans[u] += M[u] - M[v] - e[i].w;

	}

}

int n, S;

int main() {

	scanf("%d", &n);

	scanf("%d", &S);

	for (int i = 1, a, b, c; i < n; i++) {

		scanf("%d%d%d", &a, &b, &c);

		add(a, b, c);

		add(b, a, c);

	}

	dfs(S);

	printf("%lld\n", ans[S]);

	return 0;

}