/+ dub.sdl:
    name "F"
    dependency "dcomp" version=">=0.6.0"
+/

import std.stdio, std.algorithm, std.range, std.conv;
// import dcomp.foundation, dcomp.scanner;
// import dcomp.datastructure.unionfind;

int solve(bool[][] g) {
    int h = g.length.to!int;
    int w = g[0].length.to!int;
/*    foreach (v; g) {
        writeln(v.map!(x => x ? "#" : ".").join(""));
    }*/
    int[] mp = new int[w]; mp[] = 0;
    int ans = 0;
    foreach (y; 0..h) {
        mp[] += 1;
        foreach (x; 0..w) {
            if (!g[y][x]) mp[x] = 0;
        }

        int[] l = iota(w+1).array, r = iota(w+1).array;
        auto uf = UnionFind(w+1);
        int[] idx = iota(w).array;
        idx.sort!((a, b) => mp[a] > mp[b]);
        int c = 0;
//        writeln(mp);
        foreach_reverse (d; 0..h+1) {
            void merge(int a, int b) {
                int nl = min(l[uf.id[a]], l[uf.id[b]]);
                int nr = max(r[uf.id[a]], r[uf.id[b]]);
                uf.merge(a, b);
                l[uf.id[a]] = nl; r[uf.id[a]] = nr;
                ans = max(ans, (nr-nl+1)*(d+1));
//                writeln("merge ", a, " ", nr, " ", nl, " ", d);
            }
            while (c < w && mp[idx[c]] == d) {
                merge(idx[c], idx[c]+1);
                c++;
            }
        }
    }
    return ans;
}

int main() {
    auto sc = new Scanner(stdin);
    int h, w;
    sc.read(h, w);
    bool[][] g = new bool[][](h, w);
    foreach (y; 0..h) {
        string s;
        sc.read(s);
        foreach (x; 0..w) {
            g[y][x] = s[x] == '#';
        }
    }
    bool[][] g2 = new bool[][](h-1, w-1);
    foreach (y; 0..h-1) {
        foreach (x; 0..w-1) {
            g2[y][x] = ((g[y][x] + g[y+1][x] + g[y][x+1] + g[y+1][x+1]) % 2 == 0);
        }
    }
    writeln(max(h, w, solve(g2)));
    return 0;
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/datastructure/unionfind.d */
// module dcomp.datastructure.unionfind;

struct UnionFind {
    import std.algorithm : map, swap, each;
    import std.range : iota, array;
    int[] id;  
    int[][] groups;  
    int count;  
    this(int n) {
        id = iota(n).array;
        groups = iota(n).map!(a => [a]).array;
        count = n;
    }
    void merge(int a, int b) {
        if (same(a, b)) return;
        count--;
        int x = id[a], y = id[b];
        if (groups[x].length < groups[y].length) swap(x, y);
        groups[y].each!(a => id[a] = x);
        groups[x] ~= groups[y];
        groups[y] = [];
    }
    int[] group(int i) {
        return groups[id[i]];
    }
    bool same(int a, int b) {
        return id[a] == id[b];
    }
}

 

 
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/foundation.d */
// module dcomp.foundation;
 
static if (__VERSION__ <= 2070) {
    template fold(fun...) if (fun.length >= 1) {
        auto fold(R, S...)(R r, S seed) {
            import std.algorithm : reduce;
            static if (S.length < 2) {
                return reduce!fun(seed, r);
            } else {
                import std.typecons : tuple;
                return reduce!fun(tuple(seed), r);
            }
        }
    }
     
}
version (X86) static if (__VERSION__ < 2071) {
    import core.bitop : bsf, bsr, popcnt;
    int bsf(ulong v) {
        foreach (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;
    }
    int bsr(ulong v) {
        foreach_reverse (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;   
    }
    int popcnt(ulong v) {
        int c = 0;
        foreach (i; 0..64) {
            if (v & (1UL << i)) c++;
        }
        return c;
    }
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/scanner.d */
// module dcomp.scanner;

 
class Scanner {
    import std.stdio : File;
    import std.conv : to;
    import std.range : front, popFront, array, ElementType;
    import std.array : split;
    import std.traits : isSomeChar, isStaticArray, isArray; 
    import std.algorithm : map;
    File f;
    this(File f) {
        this.f = f;
    }
    char[512] lineBuf;
    char[] line;
    private bool succ() {
        import std.range.primitives : empty, front, popFront;
        import std.ascii : isWhite;
        while (true) {
            while (!line.empty && line.front.isWhite) {
                line.popFront;
            }
            if (!line.empty) break;
            if (f.eof) return false;
            line = lineBuf[];
            f.readln(line);
        }
        return true;
    }

    private bool readSingle(T)(ref T x) {
        import std.algorithm : findSplitBefore;
        import std.string : strip;
        import std.conv : parse;
        if (!succ()) return false;
        static if (isArray!T) {
            alias E = ElementType!T;
            static if (isSomeChar!E) {
                 
                 
                auto r = line.findSplitBefore(" ");
                x = r[0].strip.dup;
                line = r[1];
            } else {
                auto buf = line.split.map!(to!E).array;
                static if (isStaticArray!T) {
                     
                    assert(buf.length == T.length);
                }
                x = buf;
                line.length = 0;
            }
        } else {
            x = line.parse!T;
        }
        return true;
    }
    int read(T, Args...)(ref T x, auto ref Args args) {
        if (!readSingle(x)) return 0;
        static if (args.length == 0) {
            return 1;
        } else {
            return 1 + read(args);
        }
    }
}


 
 

 
