#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <iomanip>
#include <limits>
#include <list>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#include <set>
using namespace std;
#define MOD (long long int)(1e9+7)
#define ll long long int
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define reps(i,n) for(int i=1; i<=(int)(n); i++)
#define REP(i,n) for(int i=n-1; i>=0; i--)
#define REPS(i,n) for(int i=n; i>0; i--)
#define INF (int)(1123456789)
#define LINF (long long int)(112345678901234567)
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
#define all(v) v.begin(), v.end()

const int N = (int)3e5;

ll mpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = mpow(a,b/2); return memo*memo%MOD;}
  else return mpow(a,b-1) * a % MOD;
}
ll lpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = lpow(a,b/2); return memo*memo;}
  else return lpow(a,b-1) * a;
}
ll gcd(ll a, ll b){
  if(b==0) return a;
  else return gcd(b, a%b);
}
vector<ll> kaijo_memo;
ll kaijo(ll n){
  if(kaijo_memo.size() > n) return kaijo_memo[n];
  if(kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while(kaijo_memo.size() <= n) kaijo_memo.push_back(kaijo_memo[kaijo_memo.size()-1] * kaijo_memo.size() % MOD);
  return kaijo_memo[n];
}
vector<ll> gyaku_kaijo_memo;
ll gyaku_kaijo(ll n){
  if(gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if(gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while(gyaku_kaijo_memo.size() <= n) gyaku_kaijo_memo.push_back(gyaku_kaijo_memo[gyaku_kaijo_memo.size()-1] * mpow(gyaku_kaijo_memo.size(), MOD-2) % MOD);
  return gyaku_kaijo_memo[n];
}

ll nCr(ll n, ll r){
  if(n == r) return 1;//0個の丸と-1個の棒みたいな時に時に効く？不安.
  if(n < r || r < 0) return 0;
  ll ret = 1;
  ret *= kaijo(n); ret %= MOD;
  ret *= gyaku_kaijo(r); ret %= MOD;
  ret *= gyaku_kaijo(n-r); ret %= MOD;
  return ret;
}

int main(void){
  ll h,w;cin>>h>>w;
  vector<string> S;
  rep(i,h){
    string s; cin>>s;
    S.push_back(s);
  }
  vector<vector<ll>> hist;
  rep(i,h+1){
    hist.push_back(vector<ll>());
    rep(j,w){
      hist[i].push_back(0);
    }
  }

  rep(y,h-1){
    int wl = 0;
    int wr = 0;
    while(wr < w){
      bool eq = S[y][wl] == S[y+1][wl];
      while(wr < w && (eq == (S[y][wr] == S[y+1][wr]))){
        wr++;
      }
      while(wl < wr){
        hist[y+1][wl] = wr-wl;
        wl++;
      }
      
    }
    /*rep(j, w){
      cerr<<hist[y+1][j]<<" ";
    }
    cerr<<endl;*/
  }

  ll ans = max(h, w);
  rep(wl, w){
    vector<ll> upper,lower;
    rep(i,h+1){
      upper.push_back(i);
      lower.push_back(i);
    }
    vector<ll> height,idx;
    height.push_back(0);
    idx.push_back(0);
    reps(y,h-1){
      while(height.back() >= hist[y][wl]){
        height.pop_back();
        idx.pop_back();
      }
      lower[y] = idx.back();
      height.push_back(hist[y][wl]);
      idx.push_back(y);
    }

    height.clear();
    idx.clear();
    height.push_back(0);
    idx.push_back(h);
    REPS(y,h-1){
      while(height.back() >= hist[y][wl]){
        height.pop_back();
        idx.pop_back();
      }
      upper[y] = idx.back();
      height.push_back(hist[y][wl]);
      idx.push_back(y);
    }

    reps(y,h-1){
      chmax(ans, (upper[y] - lower[y]) * hist[y][wl]);
    }

  }
  cout<<ans<<endl;

  return 0;
}


Measured memory_bytes: 36480