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

#define i64 long long int
#define ran 101101

int n;
i64 m;
int a[ran];
i64 s[ran];

i64 calc(int lim) {
	i64 res = 0LL;
	for(int i=0;i<n;i++) {
		int p = lower_bound(a, a+n, lim-a[i]) - a;
		int cnt = n-p;
		res += cnt;
	}
	return res;
}

int main() {
	scanf("%d%lld", &n, &m);
	for(int i=0;i<n;i++) scanf("%d", &a[i]);
	sort(a,a+n);
	
	int l = 0, r = a[n-1]+a[n-1], lim = 0;
	while(l<=r) {
		int mid = (l+r)/2;
		if(calc(mid)>=m) {
			l = mid+1;
			lim = mid;
		} else r = mid-1;
	}
	s[n] = 0;
	for(int i=n-1;i>=0;i--)
		s[i] = a[i] + s[i+1];
	
	i64 ans = 0LL, tot_count = 0LL;
	for(int i=0;i<n;i++) {
		int p = lower_bound(a, a+n, lim-a[i]) - a;
		int cnt = n-p;
		ans += 1LL * a[i] * cnt;
		ans += s[p];
		tot_count += cnt;
	}
	ans -= (tot_count - m) * lim;
	printf("%lld\n", ans);
	
	return 0;
}