#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>

using namespace std;

const int MAXN = 100005;


bool Viz[MAXN];
int D[MAXN], Parent[18][MAXN];
int n;

vector<pair<int, int>> G[MAXN];


void dfs(int node) {
	Viz[node] = 1;
	for(auto vec : G[node]) {
		if(!Viz[vec.first]) {
			D[vec.first] = D[node] + vec.second;
			Parent[0][vec.first] = node;
			for(int i = 1; Parent[i - 1][vec.first]; ++i)
				Parent[i][vec.first] = Parent[i - 1][Parent[i - 1][vec.first]];

			dfs(vec.first);
		}
	}
}


int Node[MAXN];
long long solve(int k) {
	for(int i = 1; i <= n; ++i)
		Node[i] = i;

	long long ans = 0;
	for(int i = 17; i >= 0; --i) {
		for(int node = 1; node <= n; ++node)
			if(Parent[i][Node[node]] && D[node] - D[Parent[i][Node[node]]] <= k) {
				ans += (1 << i);
				Node[node] = Parent[i][Node[node]];
			}
	}

	return ans;
}

int main() {
	int a, b, c;
	long long m;
	cin >> n >> m;
	for(int i = 2; i <= n; ++i) {
		cin >> a >> b >> c;
		G[a].push_back({b, c});
		G[b].push_back({a, c});
	}

	dfs(1);

	int ans = -1;
	for(int step = (1 << 29); step; step >>= 1) {
		if(solve(step + ans) < m)
			ans += step;
	}

	if(ans > 1e9) ans = -2;

	cout << ans + 1;
	return 0;
}