835 B | 835 chars
#include <bits/stdc++.h>
#define for1(s,n) for(int i = s; i < n; i++)
#define for1j(s,n) for(int j = s; j < n; j++)
#define foreach(k) for(auto i : k)
#define foreachj(k) for(auto j : k)
#define pb(a) push_back(a)
#define sz(a) a.size()
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef vector <int> iv1;
typedef vector <vector<int>> iv2;
typedef vector <ll> llv1;
typedef unsigned int uint;
typedef vector <ull> ullv1;
typedef vector <vector <ull>> ullv2;
ll N, K, ar[22000], ans;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> K;
for1(0, N) {
cin >> ar[i];
}
sort(ar,ar+N);
for1(0, N) {
ll current = ar[i];
ll z = lower_bound(ar+i+1, ar+N, K-current+1) - (ar+i+1);
ans += z;
}
cout << ans;
}