#include <bits/stdc++.h>
using namespace std;

// template {{{
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#define f first
#define s second

#define sz(x) int((x).size())
#define all(x) (x).begin(), (x).end()

#define FOR(i, a, b)    for (int i = (a); i < (b); i++)
#define F0R(i, a)       for (int i = 0; i < (a); i++)
#define FORd(i, a, b)   for (int i = (b)-1; i >= (a); i--)
#define F0Rd(i, a)      for (int i = (a)-1; i >= 0; i--)
#define trav(a, x)      for (auto& a : x)

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vd = vector<double>;
using vs = vector<string>;

template<typename T> void ckmin(T& a, const T& b) { a = min(a, b); }
template<typename T> void ckmax(T& a, const T& b) { a = max(a, b); }

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

namespace __input {
    template<class T1, class T2> void re(pair<T1,T2>& p);
    template<class T> void re(vector<T>& a);
    template<class T, size_t SZ> void re(array<T,SZ>& a);

    template<class T> void re(T& x) { cin >> x; }
    void re(double& x) { string t; re(t); x = stod(t); }
    template<class Arg, class... Args> void re(Arg& first, Args&... rest) {
        re(first); re(rest...);
    }

    template<class T1, class T2> void re(pair<T1,T2>& p) { re(p.f,p.s); }
    template<class T> void re(vector<T>& a) { F0R(i,sz(a)) re(a[i]); }
    template<class T, size_t SZ> void re(array<T,SZ>& a) { F0R(i,SZ) re(a[i]); }
}
using namespace __input;

namespace __output {
    template<class T1, class T2> void pr(const pair<T1,T2>& x);
    template<class T, size_t SZ> void pr(const array<T,SZ>& x);
    template<class T> void pr(const vector<T>& x);
    template<class T> void pr(const set<T>& x);
    template<class T1, class T2> void pr(const map<T1,T2>& x);

    template<class T> void pr(const T& x) { cout << x; }
    template<class Arg, class... Args> void pr(const Arg& first, const Args&... rest) {
        pr(first); pr(rest...);
    }

    template<class T1, class T2> void pr(const pair<T1,T2>& x) {
        pr("{",x.f,", ",x.s,"}");
    }
    template<class T> void prContain(const T& x) {
        pr("{");
        bool fst = 1; for (const auto& a: x) pr(!fst?", ":"",a), fst = 0;
        pr("}");
    }
    template<class T, size_t SZ> void pr(const array<T,SZ>& x) { prContain(x); }
    template<class T> void pr(const vector<T>& x) { prContain(x); }
    template<class T> void pr(const set<T>& x) { prContain(x); }
    template<class T1, class T2> void pr(const map<T1,T2>& x) { prContain(x); }

    void ps() { pr("\n"); }
    template<class Arg> void ps(const Arg& first) {
        pr(first); ps();
    }
    template<class Arg, class... Args> void ps(const Arg& first, const Args&... rest) {
        pr(first," "); ps(rest...);
    }
}
using namespace __output;
// }}}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    int H, W; re(H, W); vs grid(H); re(grid);

    int ans = 0;

    vector<array<int, 2>> match(W);
    F0Rd (r0, H) {
        F0R (c, W - 1) {
            if (grid[r0][c] == grid[r0][c+1]) match[c+1][0]++;
            else match[c+1][0] = 0;

            if (grid[r0][c] != grid[r0][c+1]) match[c+1][1]++;
            else match[c+1][1] = 0;
        }

        stack<pair<int, int>> st; st.push({ H - r0, 0 });
        FOR (c, 1, W) {
            int ht = max(match[c][0], match[c][1]);
            int bg = c - 1;
            while (!st.empty() && st.top().f > ht) {
                ckmin(bg, st.top().s);
                ckmax(ans, (c - st.top().s) * st.top().f);
                st.pop();
            }
            if (st.empty() || st.top().f < ht)
                st.push({ ht, bg });
        }
        while (!st.empty()) {
            ckmax(ans, st.top().f * (W - st.top().s));
            st.pop();
        }
    }

    ps(ans);

    return 0;
}



Measured memory_bytes: 4480