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

class Main {
    static In in = new In();
    static Out out = new Out();
    static long mod = 1000000007;
    static long inf = 0xfffffffffffffffL;

    void solve() {
        int n = in.nextInt();
        long m = in.nextLong();
        long[] a = in.nextLongArray(n);
        sort(a, Comparator.reverseOrder());
        long[] b = new long[n + 1];
        for (int i = 0; i < n; i++) {
            b[i + 1] = a[i];
        }
        Arrays.parallelPrefix(b, Long::sum);
        long left = 0, right = Long.MAX_VALUE;
        while (right - left > 1) {
            long mid = (left + right) / 2;
            long ok = 0;
            for (int i = 0; i < n; i++) {
                int left2 = -1, right2 = n;
                while (right2 - left2 > 1) {
                    int mid2 = (left2 + right2) / 2;
                    if (a[mid2] + a[i] >= mid) {
                        left2 = mid2;
                    } else {
                        right2 = mid2;
                    }
                }
                ok += right2;
            }
            if (ok >= m) {
                left = mid;
            } else {
                right = mid;
            }
        }
        long ans = 0;
        long c = 0;
        for (int i = 0; i < n; i++) {
            int left2 = -1, right2 = n;
            while (right2 - left2 > 1) {
                int mid2 = (left2 + right2) / 2;
                if (a[mid2] + a[i] >= left) {
                    left2 = mid2;
                } else {
                    right2 = mid2;
                }
            }
            c += right2;
            ans += b[right2] + a[i] * right2;
        }
        ans -= (c - m) * left;
        out.println(ans);
    }

    static void sort(long[] a, Comparator<Long> comparator) {
        Long[] b = new Long[a.length];
        for (int i = 0; i < a.length; i++) {
            b[i] = a[i];
        }
        Arrays.sort(b, comparator);
        for (int i = 0; i < a.length; i++) {
            a[i] = b[i];
        }
    }

    public static void main(String[]$) {
        new Main().solve();
        out.flush();
    }
}

class In {
    private BufferedReader reader = new BufferedReader(new InputStreamReader(System.in), 0x10000);
    private StringTokenizer tokenizer;

    String next() {
        try {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                tokenizer = new StringTokenizer(reader.readLine());
            }
        } catch (IOException ignored) {
        }
        return tokenizer.nextToken();
    }

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

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

    char[][] nextCharArray(int n, int m) {
        char[][] a = new char[n][m];
        for (int i = 0; i < n; i++) {
            a[i] = next().toCharArray();
        }
        return a;
    }

    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, IntUnaryOperator op) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = op.applyAsInt(nextInt());
        }
        return a;
    }

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

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

class Out {
    private static PrintWriter out = new PrintWriter(System.out);

    void println(Object... a) {
        StringJoiner joiner = new StringJoiner(" ");
        for (Object obj : a) {
            joiner.add(String.valueOf(obj));
        }
        out.println(joiner);
    }

    void flush() {
        out.flush();
    }
}


Measured memory_bytes: 47836