#include <bits/stdc++.h>
using namespace std;

#ifdef _WIN32
#define scanfll(x) scanf("%I64d", x)
#define printfll(x) printf("%I64d", x)
#else
#define scanfll(x) scanf("%lld", x)
#define printfll(x) printf("%lld", x)
#endif
#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define repi(i,a,b) for(long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template<class T1, class T2> bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

using ll = long long; using vll = vector<ll>; using vvll = vector<vll>;
using ld = long double;  using vld = vector<ld>; 
using vi = vector<int>; using vvi = vector<vi>;
vll conv(vi& v) { vll r(v.size()); rep(i, v.size()) r[i] = v[i]; return r; }
using P = pair<ll, ll>;

template <typename T, typename U> ostream &operator<<(ostream &o, const pair<T, U> &v) {  o << "(" << v.first << ", " << v.second << ")"; return o; }
template<size_t...> struct seq{}; template<size_t N, size_t... Is> struct gen_seq : gen_seq<N-1, N-1, Is...>{}; template<size_t... Is> struct gen_seq<0, Is...> : seq<Is...>{};
template<class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch,Tr>& os, Tuple const& t, seq<Is...>){ using s = int[]; (void)s{0, (void(os << (Is == 0? "" : ", ") << get<Is>(t)), 0)...}; }
template<class Ch, class Tr, class... Args> 
auto operator<<(basic_ostream<Ch, Tr>& os, tuple<Args...> const& t) -> basic_ostream<Ch, Tr>& { os << "("; print_tuple(os, t, gen_seq<sizeof...(Args)>()); return os << ")"; }
ostream &operator<<(ostream &o, const vvll &v) { rep(i, v.size()) { rep(j, v[i].size()) o << v[i][j] << " "; cout << endl; } return o; }
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) { o << '['; rep(i, v.size()) o << v[i] << (i != v.size()-1 ? ", " : ""); o << "]";  return o; }
template <typename T>  ostream &operator<<(ostream &o, const set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U>  ostream &operator<<(ostream &o, const map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U>  ostream &operator<<(ostream &o, const unordered_map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it; o << "]";  return o; }
string bits_to_string(ll mask, ll n) { string s; rep(i, n) s += '0' + !!(mask & (1ll << i)); return s; }
#define ldout fixed << setprecision(40) 

static const double EPS = 1e-14;
static const long long INF = 1e18;
static const long long mo = 1e9+7;

int main(void) {
    cin.tie(0); ios::sync_with_stdio(false);
    ll n, m; cin >> n >> m;
    vector<unordered_map<ll,ll>> cat(m);
    rep(i, n) {
        ll tmp; cin >> tmp;
        cat[tmp % m][tmp]++;
    }
    vector<P> rem(m);
    rep(i, m) {
        for (auto& x : cat[i]) {
            rem[i].fi += x.se / 2;
            rem[i].se += x.se % 2;
        }
    }
    
//    cout << rem << endl;
    ll id = 0;
    ll ret = 0;
    rep(i, m) {
        ll corr = (m - i) % m;
        if (i == corr) {
            ret += (rem[i].fi * 2 + rem[i].se) / 2;
            rem[i].se = (rem[i].fi * 2 + rem[i].se) % 2;
            rem[i].fi = 0;
            continue;
        }
        if ((rem[i].fi == 0 && rem[i].se == 0) ||
            (rem[corr].fi == 0 && rem[corr].se == 0)) {
            continue;
        }

        // 奇数から取る
        ll i_num = rem[i].fi * 2 + rem[i].se;
        ll corr_num = rem[corr].fi * 2 + rem[corr].se;

        auto small = rem[i];
        auto large = rem[corr];
//        cout << i << " " << small << "#i " << endl;
//        cout << corr << " " << large << "#corr "<< endl;
        if (i_num > corr_num) {
            swap(small, large);
        }
        if (large.se >= small.fi * 2 + small.se) {
            large.se -= small.fi * 2 + small.se;
        } else { 
            ll large_rem =  large.fi * 2 + large.se 
                - small.fi * 2 - small.se;
            large.fi = large_rem / 2;
            large.se = large_rem % 2;
        }
//        cout << small << "#small" << endl;
        ret += small.fi * 2 + small.se;
        small.fi = 0;
        small.se = 0;

        if (i_num > corr_num) {
            swap(small, large);
        }
//        cout << i << " " << small << "#i " << endl;
//        cout << corr << " " << large << "#corr "<< endl;
        rem[i] = small;
        rem[corr] = large;
//        cout << i << " " << ret << "#ret"  << endl;
    }
//    cout << ret <<"#end"<< endl;

    rep(i, m) {
        ret += rem[i].fi;
//        cout << rem[i] << endl;
    }
    cout << ret << endl;

    return 0;
}


Measured memory_bytes: 13568