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

#define NDEBUG
#include <cassert>


typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<llll> vllll;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define eb  emplace_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define repC3(vari,varj,vark,n)  for(int vari=0;vari<(n)-2;++vari)for(int varj=vari+1;varj<(n)-1;++varj)for(int vark=varj+1;vark<(n);++vark)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair
#define clamp(v,lo,hi) min(max(v,lo),hi)

template <typename T>
inline bool found(set<T> &s, T elem) { return s.find(elem) != s.end(); }
template <typename T>
inline bool found(unordered_set<T> &s, T elem) { return s.find(elem) != s.end(); }
template <typename T, typename U>
inline bool found(map<T,U> &s, U elem) { return s.find(elem) != s.end(); }
template <typename T, typename U>
inline bool found(unordered_map<T,U> &s, U elem) { return s.find(elem) != s.end(); }
template <typename T>
inline bool found(vector<T> &s, T elem) { return find(s.begin(), s.end(), elem) != s.end(); }
inline int found(string &s, string t) { return (int)s.find(t); }
inline int found(string &s, int c) { return (int)s.find(c); }

template<typename T1, typename T2> inline void amin(T1 & a, T2 const & b) { if (a>b) a=b; }
template<typename T1, typename T2> inline void amax(T1 & a, T2 const & b) { if (a<b) a=b; }
template<typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template<typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }

inline ll square(ll x) { return x * x; }
inline ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }
template <typename T>
inline T mod(T a, T b) { return ((a % b) + b) % b; }

ll extgcd(ll a, ll b, ll &p, ll &q) {
    if (b == 0) { p = 1; q = 0; return a; }
    ll d = extgcd(b, a%b, q, p);
    q -= a/b * p;
    return d;
}

template <typename T>
int find_left(vector<T>& v, T elem) {
    return (int)(upper_bound(v.begin(), v.end(), elem) - v.begin()) - 1;
}
template <typename T>
int find_right(vector<T>& v, T elem) {
    return (int)(lower_bound(v.begin(), v.end(), elem) - v.begin());
}

const ll MOD=1000000007LL;

ll ADD(ll x, ll y) { return (x+y) % MOD; }
ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
ll MUL(ll x, ll y) { return x*y % MOD; }
ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
ll DIV(ll x, ll y) { /*assert(y%MOD!=0);*/ return MUL(x, POW(y, MOD-2)); }


ll pre_garner(vector<ll> &b, vector<ll> &m, ll mod_) {
    ll res = 1;
    rep(i, b.size()){
        rep(j, i){
            ll g = gcd(m[i], m[j]);

            if ((b[i] - b[j])%g != 0) return -1;

            m[i] /= g;
            m[j] /= g;

            ll gi = gcd(m[i], g);
            ll gj = g/gi;

            do {
                g = gcd(gi, gj);
                gi *= g;
                gj /= g;
            } while (g != 1);

            m[i] *= gi; b[i] %= m[i];
            m[j] *= gj; b[j] %= m[j];
        }
    }
    rep(i, b.size()) (res *= m[i]) %= mod_;
    return res;
}

inline ll mod_pow(ll x, ll e, ll mod_) {
 	long long v = 1LL;
	for ( ; e; e>>=1) {
		if (e & 1) v = (v * x) % mod_;
		x = (x * x) % mod_;
	}
	return v;
}

ll mod_inv(ll a, ll m) {
    ll x, y;
    extgcd(a, m, x, y);
    return mod(x, m);
}

ll garner(vector<ll> b, vector<ll> m, ll mod_) {
    m.pb(mod_);
    vector<ll> coeffs(m.size(), 1);
    vector<ll> constants(m.size(), 0);
    rep(k, b.size()) {
        ll t = mod( (b[k] - constants[k]) * mod_inv(coeffs[k], m[k]), m[k] );
        for (int i=k+1; i < (int)m.size(); ++i) {
            (constants[i] += t * coeffs[i]) %= m[i];
            (coeffs[i] *= m[k]) %= m[i];
        }
    }
    return constants.back();
}

template<typename T> inline void bit_reverse(vector<T>& a) {
    int n = a.size();
    int i = 0;
    for (int j=1; j<n-1; ++j) {
        for (int k=n>>1; k > (i ^= k); k>>=1);
        if (j < i) swap(a[i], a[j]);
    }
}

template<ll mod_, ll primitive_root>
class NTT {
public:
    ll get_mod() { return mod_; }

    void _ntt(vector<ll>& a, int sign) {
        const int n = a.size();
        assert((n ^ (n&-n)) == 0);

        const ll g = primitive_root;

        ll tmp = (mod_ - 1) * mod_inv(n, mod_) % mod_;
        ll h = mod_pow(g, tmp, mod_);
        if (sign == -1) h = mod_inv(h, mod_);

        bit_reverse(a);

        for (int m=1; m<n; m<<=1) {
            const int m2 = 2 * m;
            ll _base = mod_pow(h, n/m2, mod_);
            ll _w = 1;
            rep(x, m){
                for (int s=x; s<n; s+=m2) {
                    ll u = a[s];
                    ll d = (a[s + m] * _w) % mod_;
                    a[s] = (u+d) % mod_;
                    a[s+m] = (u-d+mod_) % mod_;
                }
                _w = (_w * _base) % mod_;
            }
        }
	}
	void ntt(vector<ll>& input) {
		_ntt(input, 1);
	}
	void intt(vector<ll>& input) {
		_ntt(input, -1);

        const ll n_inv = mod_inv(input.size(), mod_);
		for (auto &x : input) x = (x * n_inv) % mod_;
	}

	vector<ll> convolution(const vector<ll>& a, const vector<ll>& b){
        int result_size = a.size() + b.size() - 1;
        int n = 1; while (n < result_size) n <<= 1;

		vector<ll> _a = a, _b = b;
        _a.resize(n, 0);
        _b.resize(n, 0);

		ntt(_a);
		ntt(_b);
        rep(i,n) _a[i] = (_a[i] * _b[i]) % mod_;
		intt(_a);

        _a.resize(result_size);
		return _a;
	}
};

vector<ll> convolution_ntt(vector<ll>& a, vector<ll>& b, ll mod_=1224736769LL) {
    for (auto &x : a) x %= mod_;
    for (auto &x : b) x %= mod_;


    NTT<167772161, 3> ntt1;
    NTT<469762049, 3> ntt2;
    NTT<1224736769, 3> ntt3;

    vector<ll> x1 = ntt1.convolution(a, b);
    vector<ll> x2 = ntt2.convolution(a, b);
    vector<ll> x3 = ntt3.convolution(a, b);

	vector<ll> ret(x1.size());
    vector<ll> mods { 167772161, 469762049, 1224736769 };
    rep(i, x1.size()){
        vector<ll> xs { x1[i], x2[i], x3[i] };
		ret[i] = garner(xs, mods, mod_);
    }

    return ret;
}


#define INTSPACE 12
char _buf[INTSPACE*1000000 + 3];

int loadint() {
    if (fgets(_buf, INTSPACE+3, stdin)==NULL) return 0;
    return atoi(_buf);
}

int loadvec(vector<int>& v, int N=-1) {
    if (N == 0) {
        v.clear();
        return 0;
    }
    if (N == -1) {
        N = loadint();
        if (N==0) return 0;
    }
    int bufsize = INTSPACE*N + 3;
    if (fgets(_buf, bufsize, stdin)==NULL) return 0;
    v.resize(N);

    int i=0;
    bool last = false;
    for (char *p=&_buf[0]; ;) {
        char *q = p;
        while (*q > ' ') ++q;
        if (*q == 0x0D || *q == 0x0A) last = true;
        *q = 0;
        v[i++] = atoi(p);
        if (last || i == N) break;
        p = q+1;
    }
    return i;
}

ll solve(ll N, ll M, vi& a) {
    assert((int)a.size() == (int)N);
    ll amax = *max_element(ALL(a)), N2 = N*N;
    vll u(amax+1, 0);
    rep(i,N) ++u[a[i]];

    vll u2 = convolution_ntt(u, u, N2+1);
    ll ans = 0;
    for (int i=u2.size()-1; i>=0; --i) {
        if (M == 0) break;
        if (!u2[i]) continue;
        ll consume = min(M, u2[i]);
        M -= consume;
        ans += (ll)i * consume;
    }
    return ans;
}

int main() {
    int N; ll M; scanf("%d %lld%*c", &N, &M);
    vi a(N); loadvec(a,N);
    cout << solve(N,M,a) << endl;
    return 0;
}


Measured memory_bytes: 11868