import java.io.*;
import java.util.*;
import java.util.function.Function;
import java.util.function.IntPredicate;

public class Main {

    static int N;
    static long M;
    static int[] A;

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);
        N = sc.nextInt();
        M = sc.nextLong();
        A = sc.nextIntArray(N);

        System.out.println(solve());
    }

    static long solve() {
        Arrays.sort(A);
        reverse(A);

        // debug("all", all());
        // M個に含まれる最大の値を探す
        int maxv = maximize(1, A[0]*2+1, v -> {
            // v以下がM個あるかどうか
            long cnt = 0;
            int y = N-1;
            for (int x = 0; x < N; x++) {
                while( y >= 0 && A[x] + A[y] < v ) {
                    y--;
                }
                cnt += y+1;
            }
            return cnt >= M;
        });

        long[] C = new long[N+1];
        for (int i = 0; i < N; i++) {
            C[i+1] = C[i] + A[i];
        }

        // maxvより大きい値を全部足す
        int y = N-1;
        long ans = 0;
        long cnt = 0;
        for (int x = 0; x < N; x++) {
            while( y >= 0 && A[x] + A[y] <= maxv ) {
                y--;
            }
            // (x, [, y]) を足す
            ans += (long)A[x] * (y+1) + C[y+1];
            cnt += y+1;
        }

        // maxvと同じやつがM-cntだけあるはずなので足す
        ans += (long)maxv * (M-cnt);
        return ans;
    }

    static int maximize(int lo, int hi, IntPredicate p) {
        while(lo < hi) {
            int x = ((hi - lo) >>> 1) + lo;
            if( p.test(x) ) {
                lo = x + 1;
            } else {
                hi = x;
            }
        }
        return lo - 1;
    }

    static void reverse(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n / 2; i++) {
            int t = arr[i];
            arr[i] = arr[n-i-1];
            arr[n-i-1] = t;
        }
    }

    @SuppressWarnings("unused")
    static class FastScanner {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken("\n");
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

    static <A> void writeLines(A[] as, Function<A, String> f) {
        PrintWriter pw = new PrintWriter(System.out);
        for (A a : as) {
            pw.println(f.apply(a));
        }
        pw.flush();
    }

    static void writeLines(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int a : as) pw.println(a);
        pw.flush();
    }

    static void writeLines(long[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (long a : as) pw.println(a);
        pw.flush();
    }

    static int max(int... as) {
        int max = Integer.MIN_VALUE;
        for (int a : as) max = Math.max(a, max);
        return max;
    }

    static int min(int... as) {
        int min = Integer.MAX_VALUE;
        for (int a : as) min = Math.min(a, min);
        return min;
    }

    static void debug(Object... args) {
        StringJoiner j = new StringJoiner(" ");
        for (Object arg : args) {
            if (arg instanceof int[]) j.add(Arrays.toString((int[]) arg));
            else if (arg instanceof long[]) j.add(Arrays.toString((long[]) arg));
            else if (arg instanceof double[]) j.add(Arrays.toString((double[]) arg));
            else if (arg instanceof Object[]) j.add(Arrays.toString((Object[]) arg));
            else j.add(arg.toString());
        }
        System.err.println(j.toString());
    }
}


Measured memory_bytes: 38716