#include <bits/stdc++.h>
using namespace std;
const long long int mod = 1000 * 1000 * 1000 + 7;
const double PI = 3.14159265358979323846264;
const pair<long long int, long long int> steps[] = {
    {1, 0}, {0, 1}, {-1, 0}, {0, -1}, {1, -1}, {1, 1}, {-1, -1}, {-1, 1}};
template <typename... T>
void read(T&... args) {
  ((cin >> args), ...);
}
template <typename... T>
void write(T&&... args) {
  ((cout << args << " "), ...);
}
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << '\n';
  err(++it, args...);
}
void fio() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
void setUpLocal() {}
const long long int maxN = (long long int)1e6 + 7;
vector<long long int> rem(101);
long long int min(long long int a, long long int b) { return a < b ? a : b; }
void solve() {
  long long int n, k;
  cin >> n >> k;
  vector<long long int> v(n);
  for (long long int i = 0; i < n; i++) {
    cin >> v[i];
    long long int l = v[i] % k;
    rem[l]++;
  }
  long long int total = rem[0] / 2;
  bool evenK = !(k & 1);
  if (evenK) {
    total += rem[k / 2] / 2;
  }
  for (long long int i = 1; i <= k / 2; i++) {
    if (evenK and i == k / 2)
      total += 0;
    else
      total += (min(rem[i], rem[k - i]));
  }
  cout << total * 2 << '\n';
}
int32_t main() {
  fio();
  setUpLocal();
  return solve(), 0;
}
