#pragma GCC target ("avx2")
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")

#include<bits/stdc++.h>
#include<math.h>
using namespace std;

typedef long long int ll;
typedef long double ld;
typedef pair<ll, ll> pl;
typedef vector<ll> vl;
#define FD(i, r, l) for(ll i = r; i > (l); --i)

#define K first
#define V second
#define G(x) ll x; cin >> x;
#define GD(x) ld x; cin >> x;
#define GS(s) string s; cin >> s;
#define EX(x) { cout << x << '\n'; exit(0); }
#define A(a) (a).begin(), (a).end()
#define F(i, l, r) for (ll i = l; i < (r); ++i)

#define NN 200010
#define M 1000000007 // 998244353

ll n, k;
vector<pl> adj[NN];
ll ans = 0;

ll dfs(ll i, ll p) {
    ll sz = 0;
    for (auto [x, w]: adj[i]) if (x-p) {
        ll child = dfs(x, i);
        ll smol = child, large = n-child;
        if (smol > large) swap(smol, large);
        ll smhlf = (k)/2;
        
        smhlf = min(smhlf, smol);
        ans += w * smhlf * (k - smhlf);
        
        // cout << "WTF " << w << " " << smhlf << " " << k-smhlf << " , " << i << " -> " << x << " , " << w << endl;

        sz += child;
    }
    return sz+1;
}

int main(){
//    freopen("a.in", "r", stdin);
//    freopen("a.out", "w", stdout);

    ios_base::sync_with_stdio(false); cin.tie(0);
    cout << fixed << setprecision(20);
    cin >> n >> k;
    F(i, 0, n-1) {
        G(x) G(y) G(w) adj[x].emplace_back(y, w); adj[y].emplace_back(x, w);
    }
    dfs(1, 1);
    cout << ans << '\n';
}