#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


constexpr Int INF = 1001001001001001001LL;

int N;
Int T;
vector<Int> C, D;
vector<int> A, B;

vector<vector<int>> graph;

namespace brute {
Int ans;
void dfs(int u, int p, Int c, Int d) {
  if ((__int128)c * d >= T) {
    chmin(ans, d);
    return;
  }
  for (const int v : graph[u]) if (p != v) {
    dfs(v, u, min(c, C[v]), d + D[v]);
  }
}
Int run() {
  ans = INF;
  for (int u = 0; u < N; ++u) dfs(u, -1, C[u], D[u]);
  return ans;
}
}  // brute

int main() {
  for (; ~scanf("%d%lld", &N, &T); ) {
    C.resize(N);
    D.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%lld%lld", &C[u], &D[u]);
    }
    A.resize(N - 1);
    B.resize(N - 1);
    for (int i = 0; i < N - 1; ++i) {
      scanf("%d%d", &A[i], &B[i]);
      --A[i];
      --B[i];
    }
    
    graph.assign(N, {});
    for (int i = 0; i < N - 1; ++i) {
      graph[A[i]].push_back(B[i]);
      graph[B[i]].push_back(A[i]);
    }
    
    const Int ans = brute::run();
    printf("%lld\n", ans);
  }
  return 0;
}