#include <bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
#define f first
#define s second
#define pb push_back
#define yes cout << "yes" << endl;
#define YES cout << "YES" << endl;
#define no cout << "no" << endl;
#define NO cout << "NO" << endl;
void never_give_up() {
int n, k;
cin >> n >> k;
vector<int>vt(n + 1);
vector<vector<int>>arr(n + 1);
for(int i = 1; i <= n; i++){
cin >> vt[i];
}
for(int i = 1; i < n; i++){
int a, b;
cin >> a >> b;
arr[i].pb(a);
arr[i].pb(b);
}
int sum = 0, to = 0;;
for(int i = 1; i <= n; i++){
if(vt[i] + to > k){
to += vt[i];
}
else{
to = 0;
sum++;
to += vt[i];
//cout << i << endl;
}
}
cout << sum << endl;
}
void You_can_do_it() {
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int THE_wasd = 1;
//cin >> THE_wasd;
while(THE_wasd--){
never_give_up();
//You_can_do_it();
}
}
