#include <iostream>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <cstdlib>
#include <map>
#include <set>
#include <queue>
#include <vector>
#include "testlib.h"
using namespace std;
#define MOD 998244353

int main() {
    registerValidation();
    long long N = inf.readLong((long long)1, (long long)100000, "N");
    inf.readSpace();
    long long M = inf.readLong((long long)1, (long long)1000000000000, "M");
    inf.readEoln();
    vector<long long> A(N);
    A[0] = inf.readLong((long long)1, (long long)1000000000000, "A1");
    map<long long, long long> Map2;
    Map2[A[0]]++;
    for (int i = 1; i < N; i++) {
        inf.readSpace();
        A[i] = inf.readLong((long long)1, (long long)1000000000000, "A");
        Map2[A[i]]++;
        if (Map2[A[i]] > 1) cout << -1 << endl;
    }
    inf.readEoln();
    inf.readEof();

	map<long long, long long> Map;
	set<long long> Set;
	for (int i = 0; i < N; i++) {
		Map[A[i] % M]++;
		Set.insert(A[i] % M);
	}

	long long count = 0;
	while (!Set.empty()) {
		long long a = *Set.begin();
		Set.erase(Set.begin());
		count += max(Map[a], Map[M - a]);
		Map[a] = 0;
		Map[M - a] = 0;
	}

	cout << count << endl;
}