#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
 
long long int INF = 1e18;
const ll fact_table = 5000000;
double Pi = 3.1415926535897932384626;
 
vector<ll> G[550010];
vector<ll> R[550010];
vector<pair<ll, double> > tree[500010];
priority_queue <ll> pql;
priority_queue <P> pqp;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
ll dx[8]={1,0,-1,0,1,1,-1,-1};
ll dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//ll bit[500005];
//↓,→,↑,←
 
 
#define p(x) cout<<x<<"\n";
#define el cout<<"\n";
#define pe(x) cout<<(x)<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
 
 
ll mod = 998244353;
//ll mod = 1000000007;
 
ll rui(ll number1,ll number2){
 
    if(number2 == 0){
        return 1;
    }else{
        ll number3 = rui(number1,number2 / 2);
        number3 *= number3;
        number3 %= mod;
        if(number2%2==1){
            number3 *= number1;
            number3 %= mod;
        }
        return number3;
    }
}
ll gcd(ll number1,ll number2){
 
    if(number1 > number2){
        swap(number1,number2);
    }
    if(number1 == 0 || number1 == number2){
        return number2;
    }else{
        return gcd(number2 % number1,number1);
    }
}
void YES(bool condition){
 
    if(condition){
        p("YES");
    }else{
        p("NO");
    }
    return;
}
void Yes(bool condition){
 
    if(condition){
        p("Yes");
    }else{
        p("No");
    }
    return;
}
 
/*
ll fact[fact_table + 5],rfact[fact_table + 5];
 
void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=fact_table; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[fact_table] = rui(fact[fact_table],mod - 2);
    for(ll i=fact_table; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod ) * rfact[n-r]) % mod;}
*/
 
ll n,m,num,sum,a,b,c,d,e,f,g,h,w,i,j,q,r,l;
ll k,ans;
ll x[500005],y[500005],z[500005];
ll dp[5005][5005];
char s[500005];
char t[500005];
bool used[500005];

bool count(ll mid){
    // 和がmid以上になるペアがm個以下であるか？
    ll okidx = n - 1;
    ll cnt = 0;
    for(ll i=0;i<n;i++){
        if(x[0] + x[i] >= mid){
            cnt += n;
            continue;
        }else if(x[n-1] + x[i] < mid){
            continue;
        }
        while(x[okidx] + x[i] >= mid){
            okidx --;
        }
        okidx ++;
        cnt += n - okidx;
    }
    if(cnt <= m){
        return true;
    }else{
        return false;
    }
}

void solve(ll mid){
    // 和がmid以上になるようにようにとった時の個数をメモ
    ll okidx = n - 1;
    for(ll i=0;i<n;i++){
        if(x[0] + x[i] >= mid){
            y[i] = n;
            continue;
        }else if(x[n-1] + x[i] < mid){
            y[i] = 0;
            continue;
        }
        while(x[okidx] + x[i] >= mid){
            okidx --;
        }
        okidx ++;
        y[i] = n - okidx;
    }
    return;
}
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    cin >> n >> m;
    for(ll i=0;i<n;i++){
        cin >> x[i];
    }
    sort(x, x + n);
    ll ok = INF, ng = 0;
    while(ok - ng > 1){
        ll mid = (ok + ng) / 2;
        bool res = count(mid);
        if(res){
            ok = mid;
        }else{
            ng = mid;
        }
    }
    solve(ok);
    for(ll i=0;i<n;i++){
        z[i] = x[i];
    }
    for(ll i=n-1;i>=1;i--){
        z[i-1] += z[i];
    }
    ll ans = 0;
    ll sum = 0;
    for(ll i=0;i<n;i++){
        //pe(y[i]);
        sum += y[i];
        if(y[i] == 0)continue;
        ans += z[n - y[i]];
        ans += x[i] * y[i];
    }
    if(sum < m){
        ans += (m - sum) * ng;
    }
    p(ans);

    return 0;
}















Measured memory_bytes: 44032