Problem: We have a board with an H \times W grid. Each square in the grid is painted in black or white. The square at the i-th row from the top and j-th column from the left is black if the j-th character in S_i is `#`, and white if that character is `.`.

Snuke can perform the following operation on the grid any number of times:

* Select a row or column in the grid, and invert the color of all the squares in that row or column (that is, black squares become white and vice versa).



Then, Snuke draws a rectangle along grid lines. Here, all the squares contained in the rectangle must be painted in black.

Find the maximum possible area of Snuke's rectangle when the operation is performed optimally.

Constraints

* 2 \leq H \leq 2000
* 2 \leq W \leq 2000
* |S_i| = W
* S_i consists of `#` and `.`.

Input

Input is given from Standard Input in the following format:


H W
S_1
S_2
:
S_H


Output

Print the maximum possible area of Snuke's rectangle.

Examples

Input

3 3
..#
##.
.#.


Output

6


Input

3 3
..#
.
.#.


Output

6


Input

4 4
....
....
....
....


Output

16


Input

10 8
...#.#
...#.#
..###.#.
.##.#.#
.#..#.#.
..##.#.#
.#.#..
...#.#..
.#.##
..###


Output

27

Solution (in JAVA):

Solution:
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.Comparator;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        TaskF solver = new TaskF();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskF {
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            int n = in.nextInt(), m = in.nextInt();
            char[][] s = new char[n][m];
            for (int i = 0; i < n; i++) s[i] = in.next().toCharArray();
//        for (int i = 0; i < n; i++) {
//            if (s[i][0] == '.') {
//                for (int j = 0; j < m; j++) {
//                    s[i][j] = (char)('#' + '.' - s[i][j]);
//                }
//            }
//        }
//        for (int i = 0; i < m; i++) {
//            if (s[0][i] == '.') {
//                for (int j = 0; j < n; j++) {
//                    s[j][i] = (char)('#' + '.' - s[j][i]);
//                }
//            }
//        }
            int ans = Math.max(n, m);
            int[][] dp = new int[n][m];
            int[][] pr = new int[n][m];
            for (int col = 1; col < m; col++) {
                dp[0][col] = 1;
                pr[0][col] = (s[0][col] == s[0][col - 1]) ? 1 : 0;
                for (int row = 1; row < n; row++) {
                    pr[row][col] = (s[row][col] == s[row][col - 1]) ? 1 : 0;
                    if (pr[row][col] == pr[row - 1][col]) dp[row][col] = dp[row - 1][col] + 1;
                    else dp[row][col] = 1;
                }
            }
            int[][] imos = new int[n + 3][m + 3];
            for (int i = 0; i < n; i++) {
                paint(dp[i], imos);
            }


            long count = 0;
            for (int i = 1; i <= n; i++) {
                for (int j = 1; j <= m + 1; j++) {
                    imos[i][j] += imos[i][j - 1];
                }
                for (int j = 1; j <= m + 1; j++) {
                    imos[i][j] += imos[i][j - 1];
                }
            }
            for (int j = 1; j <= m; j++) {
                for (int i = n; i >= 1; i--) {
                    imos[i][j] += imos[i + 1][j];
                }
            }
            for (int i = 1; i <= n; i++)
                for (int j = 1; j <= m; j++) {
                    if (imos[i][j] > 0) ans = Math.max(ans, i * (j + 1));
                }
            out.println(ans);
        }

        static void paint(int[] up, int[][] imos) {
            int m = up.length;
            int[][] ups = new int[m][];
            for (int i = 0; i < m; i++) ups[i] = new int[]{up[i], i};
            Arrays.sort(ups, new Comparator<int[]>() {
                public int compare(int[] a, int[] b) {
                    if (a[0] != b[0]) return a[0] - b[0];
                    return a[1] - b[1];
                }
            });
            TaskF.LST lst = new TaskF.LST(m);
            for (int[] u : ups) {
                if (u[0] > 0) {
                    int bef = lst.prev(u[1]);
                    int aft = lst.next(u[1]);
                    if (aft == -1) aft = m;
                    int bd = u[1] - bef - 1;
                    int ad = aft - u[1] - 1;
//				tr(u, bef, aft, bd, ad);

                    imos[u[0]][1]++;
                    imos[u[0]][bd + ad + 1 + 2]--;
                    imos[u[0]][bd + 1 + 1]--;
                    imos[u[0]][bd + ad + 1 + 2]++;
                    imos[u[0]][ad + 1 + 1]--;
                    imos[u[0]][bd + ad + 1 + 2]++;
                }
                lst.set(u[1]);
            }
        }

        public static class LST {
            public long[][] set;
            public int n;

            public LST(int n) {
                this.n = n;
                int d = 1;
                for (int m = n; m > 1; m >>>= 6, d++) ;

                set = new long[d][];
                for (int i = 0, m = n >>> 6; i < d; i++, m >>>= 6) {
                    set[i] = new long[m + 1];
                }
//			size = 0;
            }

            public TaskF.LST set(int pos) {
                if (pos >= 0 && pos < n) {
//				if(!get(pos))size++;
                    for (int i = 0; i < set.length; i++, pos >>>= 6) {
                        set[i][pos >>> 6] |= 1L << pos;
                    }
                }
                return this;
            }

            public int prev(int pos) {
                for (int i = 0; i < set.length && pos >= 0; i++, pos >>>= 6, pos--) {
                    int pre = prev(set[i][pos >>> 6], pos & 63);
                    if (pre != -1) {
                        pos = pos >>> 6 << 6 | pre;
                        while (i > 0) pos = pos << 6 | 63 - Long.numberOfLeadingZeros(set[--i][pos]);
                        return pos;
                    }
                }
                return -1;
            }

            public int next(int pos) {
                for (int i = 0; i < set.length && pos >>> 6 < set[i].length; i++, pos >>>= 6, pos++) {
                    int nex = next(set[i][pos >>> 6], pos & 63);
                    if (nex != -1) {
                        pos = pos >>> 6 << 6 | nex;
                        while (i > 0) pos = pos << 6 | Long.numberOfTrailingZeros(set[--i][pos]);
                        return pos;
                    }
                }
                return -1;
            }

            private static int prev(long set, int n) {
                long h = Long.highestOneBit(set << ~n);
                if (h == 0L) return -1;
                return Long.numberOfTrailingZeros(h) - (63 - n);
            }

            private static int next(long set, int n) {
                long h = Long.lowestOneBit(set >>> n);
                if (h == 0L) return -1;
                return Long.numberOfTrailingZeros(h) + n;
            }

        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (this.numChars == -1) {
                throw new InputMismatchException();
            } else {
                if (this.curChar >= this.numChars) {
                    this.curChar = 0;

                    try {
                        this.numChars = this.stream.read(this.buf);
                    } catch (IOException var2) {
                        throw new InputMismatchException();
                    }

                    if (this.numChars <= 0) {
                        return -1;
                    }
                }

                return this.buf[this.curChar++];
            }
        }

        public int nextInt() {
            int c;
            for (c = this.read(); isSpaceChar(c); c = this.read()) {
                ;
            }

            byte sgn = 1;
            if (c == 45) {
                sgn = -1;
                c = this.read();
            }

            int res = 0;

            while (c >= 48 && c <= 57) {
                res *= 10;
                res += c - 48;
                c = this.read();
                if (isSpaceChar(c)) {
                    return res * sgn;
                }
            }

            throw new InputMismatchException();
        }

        public String next() {
            int c;
            while (isSpaceChar(c = this.read())) {
                ;
            }

            StringBuilder result = new StringBuilder();
            result.appendCodePoint(c);

            while (!isSpaceChar(c = this.read())) {
                result.appendCodePoint(c);
            }

            return result.toString();
        }

        public static boolean isSpaceChar(int c) {
            return c == 32 || c == 10 || c == 13 || c == 9 || c == -1;
        }

    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void close() {
            writer.close();
        }

        public void println(int i) {
            writer.println(i);
        }

    }
}