import java.io.*;
import java.util.*;
import java.math.*;
// import java.awt.Point;
 
public class Main {
    InputStream is;
    PrintWriter out;
    String INPUT = "";
 
    long MOD = 1_000_000_007;
    int inf = Integer.MAX_VALUE/2;

    void solve(){
        int x = ni();
        int y = ni();
        char[][] map = nm(x,y);
        int[] dx = {0,0,1,1};
        int[] dy = {0,1,0,1};
        int[][] nmap = new int[x-1][y-1];
        for(int i = 0; i < x-1; i++){
            for(int j = 0; j < y-1; j++){
                int a = 0;
                for(int k = 0; k < 4; k++){
                    int cx = i + dx[k];
                    int cy = j + dy[k];
                    if(map[cx][cy]=='.') a++;
                }
                if(a%2==0) nmap[i][j] = 1;
                else nmap[i][j] = 0;
            }
        }
        long ans = maxRect(nmap[0]);
        for(int i = 1; i < x-1; i++){
            for(int j = 0; j < y-1; j++){
                if(nmap[i][j]==1) nmap[i][j] += nmap[i-1][j];
            }
            ans = Math.max(ans, maxRect(nmap[i]));
        }
        ans = Math.max(x,ans);
        ans = Math.max(y,ans);
        out.println(ans);
    }

    public static long maxRect(int[] a)
    {
        int n = a.length;
        int[] stack = new int[n];
        int[] left = new int[n];
        int p = 0;
        long max = 0;
        for(int i = 0;i < n;i++){
            int o = p;
            while(p > 0 && stack[p-1] >= a[i]){
                p--;
                max = Math.max(max, (long)(i-1-left[p]+1+1)*(stack[p]+1));
            }
            if(o == p)left[p] = i;
            stack[p++] = a[i];
        }
        while(p > 0){
            p--;
            max = Math.max(max, (long)(n-1-left[p]+1+1)*(stack[p]+1));
        }
        return max;
    }


    void run() throws Exception
    {
        is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        solve();
        out.flush();
        if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
    }
    
    public static void main(String[] args) throws Exception { new Main().run(); }
    
    private byte[] inbuf = new byte[1024];
    private int lenbuf = 0, ptrbuf = 0;
    
    private int readByte()
    {
        if(lenbuf == -1)throw new InputMismatchException();
        if(ptrbuf >= lenbuf){
            ptrbuf = 0;
            try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
            if(lenbuf <= 0)return -1;
        }
        return inbuf[ptrbuf++];
    }
    
    private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
    private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
    
    private double nd() { return Double.parseDouble(ns()); }
    private char nc() { return (char)skip(); }
    
    private String ns()
    {
        int b = skip();
        StringBuilder sb = new StringBuilder();
        while(!(isSpaceChar(b) && b != ' ')){
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    
    private char[] ns(int n)
    {
        char[] buf = new char[n];
        int b = skip(), p = 0;
        while(p < n && !(isSpaceChar(b))){
            buf[p++] = (char)b;
            b = readByte();
        }
        return n == p ? buf : Arrays.copyOf(buf, p);
    }
    
    private char[][] nm(int n, int m)
    {
        char[][] map = new char[n][];
        for(int i = 0;i < n;i++)map[i] = ns(m);
        return map;
    }
    
    private int[] na(int n)
    {
        int[] a = new int[n];
        for(int i = 0;i < n;i++)a[i] = ni();
        return a;
    }
    
    private int ni()
    {
        int num = 0, b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-'){
            minus = true;
            b = readByte();
        }
        
        while(true){
            if(b >= '0' && b <= '9'){
                num = num * 10 + (b - '0');
            }else{
                return minus ? -num : num;
            }
            b = readByte();
        }
    }
    
    private long nl()
    {
        long num = 0;
        int b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-'){
            minus = true;
            b = readByte();
        }
        
        while(true){
            if(b >= '0' && b <= '9'){
                num = num * 10 + (b - '0');
            }else{
                return minus ? -num : num;
            }
            b = readByte();
        }
    }
    
    private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
 
}

Measured memory_bytes: 72532