/*** Template Begin ***/

#define USING_BOOST
#define USING_NAMESPACE

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

typedef long long i64;

auto init_ = [] {
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed;
    return 0;
}();

template <typename T>
inline void in(T &x) {
    std::cin >> x;
}

template <typename T, typename... Ts>
inline void in(T &t, Ts &... ts) {
    std::cin >> t;
    in(ts...);
}

template <typename T, typename U = std::vector<T>>
inline U vin(int n) {
    U v(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> v[i];
    }
    return v;
}

template <typename T, typename U = std::vector<T>, typename V = std::vector<U>>
inline V vin(int h, int w) {
    V vv(h, U(w));
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            std::cin >> vv[i][j];
        }
    }
    return vv;
}

template <typename T>
inline void out(const T &x) {
    std::cout << x << std::endl;
}

template <char delimiter = ' ', typename T, typename... Ts>
inline void out(const T &t, const Ts &... ts) {
    std::cout << t << delimiter;
    out(ts...);
}

template <char delimiter = ' ', typename T>
inline void vout(const T &v, int n) {
    for (int i = 0; i < n; ++i) {
        if (i) std::cout << delimiter;
        std::cout << v[i];
    }
    std::cout << std::endl;
}

template <char delimiter = ' ', typename T>
inline void vout(const T &v, int h, int w) {
    for (int i = 0; i < h; ++i) {
        for (int j = 0; j < w; ++j) {
            if (j) std::cout << delimiter;
            std::cout << v[i][j];
        }
        std::cout << std::endl;
    }
}

template <typename T, size_t D>
struct multi_vector_type {
    using type = std::vector<typename multi_vector_type<T, D - 1>::type>;
};

template <typename T>
struct multi_vector_type<T, 1> {
    using type = std::vector<T>;
};

template <typename T>
struct multi_vector_type<T, 0> {
    using type = T;
};

template <typename T, size_t D>
using multi_vector = typename multi_vector_type<T, D>::type;

template <typename T, size_t D, class = typename std::enable_if<D == 0>::type>
T make_vector(const T &val = T()) {
    return val;
}

template <typename T, size_t D = 1, typename... Ts,
          class = typename std::enable_if<D != 0>::type>
multi_vector<T, D> make_vector(size_t n, Ts &&... args) {
    return multi_vector<T, D>(n, make_vector<T, D - 1>(args...));
}

namespace detail {

template <typename F>
struct Debug {
    const char *delim_ = "\n";
    F fun;

    Debug(F f) : fun(f) {}

    ~Debug() { fun(delim_); }

    Debug &delim(const char *d) {
        delim_ = d;
        return *this;
    }
};

std::deque<std::string> split(const std::string &s, char c) {
    std::deque<std::string> v;
    std::stringstream ss(s);
    std::string x;
    while (std::getline(ss, x, c)) v.emplace_back(x);
    return v;
}

template <typename T>
void deb(const char *delim, std::deque<std::string> v, T a) {
    std::cerr << v[0].substr(v[0][0] == ' ', v[0].length()) << " = " << a
              << '\n';
    std::cerr << std::flush;
}

template <typename T, typename... Args>
void deb(const char *delim, std::deque<std::string> v, T a, Args... args) {
    std::cerr << v[0].substr(v[0][0] == ' ', v[0].length()) << " = " << a
              << delim;
    v.pop_front();
    deb(delim, std::move(v), args...);
}

template <typename... Args>
auto wrap(std::deque<std::string> v, Args... args) {
    auto f = [=](const char *delim = "\n") { deb(delim, v, args...); };

    return Debug<decltype(f)>(f);
}
}

#define debug(args...) ::detail::wrap(::detail::split(#args, ','), args)

#ifdef USING_BOOST

#include <boost/math/common_factor.hpp>
#include <boost/range.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/algorithm.hpp>
#include <boost/range/algorithm_ext.hpp>
#include <boost/range/irange.hpp>
#include <boost/range/numeric.hpp>

inline auto rep(int begin, int end) {
    if (begin > end) {
        return boost::irange(0, 0);
    } else {
        return boost::irange(begin, end);
    }
}

inline auto rep(int begin, int end, int step) {
    if ((step > 0 && begin > end) || (step < 0 && begin < end)) {
        return boost::irange(0, 0, step);
    } else {
        return boost::irange(begin, end, step);
    }
}

#endif

#ifdef USING_NAMESPACE
using namespace std;

#ifdef USING_BOOST
using namespace boost;
using namespace boost::adaptors;
#endif
#endif

/*** Template End ***/

i64 histgram(int n, const vector<int> &h) {
    vector<int> L(n), R(n);

    stack<int> s;
    for (int i = 0; i < n; ++i) {
        while (!s.empty() && h[s.top()] >= h[i]) {
            s.pop();
        }

        L[i] = s.empty() ? 0 : (s.top() + 1);
        s.push(i);
    }

    s = stack<int>();
    for (int i = n - 1; i >= 0; i--) {
        while (!s.empty() && h[s.top()] >= h[i]) {
            s.pop();
        }

        R[i] = s.empty() ? n : s.top();
        s.push(i);
    }

    i64 res = 0;
    for (int i = 0; i < n; ++i) {
        res = max(res, (i64)h[i] * (R[i] - L[i]));
    }

    return res;
}

i64 histgram2(int n, const vector<int> &h) {
    vector<int> L(n), R(n);

    stack<int> s;
    for (int i = 0; i < n; ++i) {
        while (!s.empty() && h[s.top()] >= h[i]) {
            s.pop();
        }

        L[i] = s.empty() ? 0 : (s.top() + 1);
        s.push(i);
    }

    s = stack<int>();
    for (int i = n - 1; i >= 0; --i) {
        while (!s.empty() && h[s.top()] >= h[i]) {
            s.pop();
        }

        R[i] = s.empty() ? n : s.top();
        s.push(i);
    }

    i64 res = 0;
    for (int i = 0; i < n; ++i) {
        res = max(res, (i64)(h[i] + 1) * (R[i] - L[i] + 1));
    }

    return res;
}

int main() {
    int h, w;
    in(h, w);

    auto s = vin<string>(h);

    auto a = make_vector<int, 2>(h - 1, w - 1);

    for (int i : rep(0, h - 1)) {
        for (int j : rep(0, w - 1)) {
            int cnt = 0;
            cnt += s[i][j] == '#';
            cnt += s[i][j + 1] == '#';
            cnt += s[i + 1][j] == '#';
            cnt += s[i + 1][j + 1] == '#';

            if (cnt & 1) {
                a[i][j] = 0;
            } else {
                a[i][j] = 1;
            }
        }
    }

    for (int j : rep(0, w - 1)) {
        for (int i : rep(1, h - 1)) {
            if (a[i][j] != 0) {
                a[i][j] += a[i - 1][j];
            }
        }
    }

    i64 ans = max(h, w);
    for (int i : rep(0, h - 1)) {
        ans = max(ans, histgram2(w - 1, a[i]));
    }

    out(ans);
}

Measured memory_bytes: 22016