#include <bits/stdc++.h>

using namespace std;

typedef long long               ll;
typedef long double             ld;


#define si(a)            scanf("%d", &a)
#define si2(a,b)         scanf("%d %d", &a,&b)
#define sll(a)           scanf("%I64d",&a)
#define sll2(a,b)        scanf("%I64d %I64d",&a,&b)
#define pb               push_back
#define pi(a)            printf("%d",a)
#define pll(a)           printf("%I64d",a)
#define ps               printf(" ")
#define nln              printf("\n")
#define vi               vector<int>
#define vll              vector<ll>
#define vstr             vector<string>
#define PI               acos(-1)
#define sq(x)            x*x
#define forr(i,a,b)      for(ll i=a;i<b;i++)
#define max3(a,b,c)      max(a,max(b,c))
#define max4(a,b,c,d)    max(max3(a,b,c),d)
#define min3(a,b,c)      min(a,min(b,c))
#define mod              1000000007

vll p(105,0);

int main()
{
    ll n,k;
    sll2(n,k);
    vll v;
    while(n--)
    {
        ll x;
        sll(x);
        v.pb(x);
    }

    forr(i,0,v.size())
    {
        ll q=v[i]%k;
        p[q]++;
    }

    ll cnt=0;
    cnt+=p[0]/2;
    forr(i,1,k)
    {
        //ll m=k-1;
        if(k-i<i) break;
        else if(k-i==i) cnt+=p[i]/2;
        else
        {
            ll c=min(p[i],p[k-i]);
            cnt+=c;

        }

    }

//    forr(i,0,k) pll(p[i]),ps;
//    nln;




    pll(cnt*2);



}



///    Before submission=>
///    ***check for integer overflow,array bounds
///    ***check for n=1