#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rrep(i,n) for(int (i)=((n)-1);(i)>=0;(i)--)
#define itn int
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
const long long INF = 1LL << 60;
const int MOD = 1000000007;
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
//https://www.creativ.xyz/dump-cpp-652/
#define repi(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
 
// vector
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}
// pair
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}
// vector
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
    os << "{";
    for (int i = 0; i < vec.size(); i++) {
        os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
    }
    os << "}";
    return os;
}
// map
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
    os << "{";
    repi(itr, map_var) {
        os << *itr;
        itr++;
        if (itr != map_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
// set
template <typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
    os << "{";
    repi(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}
 
#define DUMPOUT cerr
 
void dump_func() {
    DUMPOUT << endl;
}
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) {
        DUMPOUT << ", ";
    }
    dump_func(std::move(tail)...);
}

#ifdef DEBUG_
#define DEB
#define dump(...)                                                              \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                            \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]"        \
            << endl                                                            \
            << "    ",                                                         \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif
template<class T>
vector <T> ruiseki(vector <T> &a){
    int sz = a.size()+1;
    vector <T> s(sz);
    for(int i=1;i<sz;i++) s[i] = s[i-1] + a[i-1];
    return s;
}
signed main(void) { cin.tie(0); ios::sync_with_stdio(false);
    int n,m; cin>>n>>m;
    vector <int> a(n);
    vector <int> data(214514);
    rep(i,n) {cin>>a[i]; data[a[i]]++;}
    sort(a.begin(),a.end(),greater<int>());
    int ans = 0;
    auto rdata = ruiseki(data);
    auto ra = ruiseki(a);
    int l = -1, r = 214514;
    
    while(abs(l - r)>1){
        
        int mid = (r+l)/2;
        int cnt = 0;
        int tans = 0;
        
        rep(i,n){
            int tmp = n - rdata[max(mid - a[i] + 1, 0LL)];
            cnt += tmp;
        }
        dump(cnt, mid);
        if(cnt >= m) {
            l = mid;
        }else{
            r = mid;
        }
    }
    int x = l+1;
    //lはm通り以上を作れる最小のX
    int mm=0;
    priority_queue <int, vector <int>, greater <int>> pq;
    rep(i,n){
        int tmp = n - rdata[max(x - a[i] + 1, 0LL)];
        mm+=tmp;
        ans += ra[tmp] + (tmp*a[i]);
    }
    //cout<<ans<<' '<<l<<endl;
    //cout<<mm<<endl;
    ans += (m - mm)*(l+1);
    cout<<ans<<endl;
}


Measured memory_bytes: 5248