#include <algorithm>

#include <cstdio>

#define maxn 100010

const long long inf = 0x3f3f3f3f3f3f3f3f;

int head[maxn], cnt;

struct Edge {

	int to, nxt, w;

} e[maxn << 1];

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

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

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

}

int n, rt, ind[maxn];

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

	long long res = 0;

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

		v = e[i].to;

		if (v != fa) res += std::min(dfs(v, u), static_cast<long long> (e[i].w));

	}

	if (u != rt && ind[u] == 1) return inf;

	return res;

}

int main() {

	scanf("%d%d", &n, &rt);

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

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

		addedge(a, b, c);

		++ind[a], ++ind[b];

	}

	printf("%lld\n", dfs(rt));

	return 0;

}