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

public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        while (true) {
            int d = sc.nextInt();
            int w = sc.nextInt();
            if (d == 0 && w == 0) {
                return;
            }
            int[][] res = new int[d][w];
            for (int i = 0; i < d; i++) {
                for (int j = 0; j < w; j++) {
                    res[i][j] = sc.nextInt();
                }
            }
            long ans = 0;
            for (int i = 0; i < d; i++) {
                for (int j = 0; j < w; j++) {
                    for (int k = i + 2; k < d; k++) {
                        for (int l = j + 2; l < w; l++) {
                            int min = 10;
                            for (int a = i; a < k + 1; a++) {
                                min = Math.min(Math.min(min, res[a][j]), res[a][l]);
                            }
                            for (int a = j; a < l + 1; a++) {
                                min = Math.min(Math.min(min, res[i][a]), res[k][a]);
                            }
                            int max = 0;
                            for (int a = i + 1; a < k; a++) {
                                for (int b = j + 1; b < l; b++) {
                                    max = Math.max(max, res[a][b]);
                                }
                            }
                            if (max >= min) {
                                continue;
                            }
                            long res1 = 0;
                            for (int a = i + 1; a < k; a++) {
                                for (int b = j + 1; b < l; b++) {
                                    res1 += Math.max(0, min - res[a][b]);
                                }
                            }
                            ans = Math.max(ans, res1);
                        }
                    }
                }
            }
            System.out.println(ans);
        }
    }
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
}



Measured memory_bytes: 28944