#include <bits/stdc++.h>
using namespace std;
vector <int> x[100500];
bool pr[100500];
int q, b, n, m, ans, a[100500];
int dfs(int v, int cnt){
  pr[v] = 1;
  if(v != 1 && a[v] != 1){
    ans++;
  }
  if(a[v] == 1){
      cnt++;
  }
  for(int i = 0; i < x[v].size(); i++){
    int d = cnt;
    if(!pr[x[v][i]] && d <= m){
      cout << v << " " << x[v][i] << endl;
      d++;
      dfs(x[v][i], d);
    }
  }
}
int main(){
  cin >> n >> m;
  for(int i = 0; i < n; i++){
    cin >> a[i];
  }
  for(int i = 0; i < n - 1; i++){
    cin >> q >> b;
    x[q].push_back(b);
    x[b].push_back(q);
  }
  dfs(1, 0);
  cout << ans;
  return 0;
}