//start of jonathanirvings' template v3.0.3 (BETA)

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

typedef long long LL;
typedef pair<int,int> pii;
typedef pair<LL,LL> pll;
typedef pair<string,string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<LL> vl;
typedef vector<vl> vvl;

double EPS = 1e-9;
int INF = 1000000005;
long long INFF = 1000000000000000005LL;
double PI = acos(-1);
int dirx[8] = {-1,0,0,1,-1,-1,1,1};
int diry[8] = {0,1,-1,0,-1,1,-1,1};

#ifdef TESTING
  #define DEBUG fprintf(stderr,"====TESTING====\n")
  #define VALUE(x) cerr << "The value of " << #x << " is " << x << endl
  #define debug(...) fprintf(stderr, __VA_ARGS__)
#else
  #define DEBUG 
  #define VALUE(x)
  #define debug(...)
#endif

#define FOR(a,b,c) for (int (a)=(b);(a)<(c);++(a))
#define FORN(a,b,c) for (int (a)=(b);(a)<=(c);++(a))
#define FORD(a,b,c) for (int (a)=(b);(a)>=(c);--(a))
#define FORSQ(a,b,c) for (int (a)=(b);(a)*(a)<=(c);++(a))
#define FORC(a,b,c) for (char (a)=(b);(a)<=(c);++(a))
#define FOREACH(a,b) for (auto &(a) : (b))
#define REP(i,n) FOR(i,0,n)
#define REPN(i,n) FORN(i,1,n)
#define MAX(a,b) a = max(a,b)
#define MIN(a,b) a = min(a,b)
#define SQR(x) ((LL)(x) * (x))
#define RESET(a,b) memset(a,b,sizeof(a))
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ALL(v) v.begin(),v.end()
#define ALLA(arr,sz) arr,arr+sz
#define SIZE(v) (int)v.size()
#define SORT(v) sort(ALL(v))
#define REVERSE(v) reverse(ALL(v))
#define SORTA(arr,sz) sort(ALLA(arr,sz))
#define REVERSEA(arr,sz) reverse(ALLA(arr,sz))
#define PERMUTE next_permutation
#define TC(t) while(t--)

inline string IntToString(LL a){
  char x[100];
  sprintf(x,"%lld",a); string s = x;
  return s;
}

inline LL StringToInt(string a){
  char x[100]; LL res;
  strcpy(x,a.c_str()); sscanf(x,"%lld",&res);
  return res;
}

inline string GetString(void){
  char x[1000005];
  scanf("%s",x); string s = x;
  return s;
}

inline string uppercase(string s){
  int n = SIZE(s); 
  REP(i,n) if (s[i] >= 'a' && s[i] <= 'z') s[i] = s[i] - 'a' + 'A';
  return s;
}

inline string lowercase(string s){
  int n = SIZE(s); 
  REP(i,n) if (s[i] >= 'A' && s[i] <= 'Z') s[i] = s[i] - 'A' + 'a';
  return s;
}

inline void OPEN (string s) {
  #ifndef TESTING
  freopen ((s + ".in").c_str (), "r", stdin);
  freopen ((s + ".out").c_str (), "w", stdout);
  #endif
}

//end of jonathanirvings' template v3.0.3 (BETA)

int r,c;
string data[2005];
int atas[2005][2005];
int hist[2005];

int getMaxArea()
{
  int n = c - 1;
    // Create an empty stack. The stack holds indexes of hist[] array
    // The bars stored in stack are always in increasing order of their
    // heights.
    stack<int> s;
 
    int max_area = 0; // Initalize max area
    int tp;  // To store top of stack
    int area_with_top; // To store area with top bar as the smallest bar
 
    // Run through all bars of given histogram
    int i = 0;
    while (i < n)
    {
        // If this bar is higher than the bar on top stack, push it to stack
        if (s.empty() || hist[s.top()] <= hist[i])
            s.push(i++);
 
        // If this bar is lower than top of stack, then calculate area of rectangle 
        // with stack top as the smallest (or minimum height) bar. 'i' is 
        // 'right index' for the top and element before top in stack is 'left index'
        else
        {
            tp = s.top();  // store the top index
            s.pop();  // pop the top
 
            // Calculate the area with hist[tp] stack as smallest bar
            area_with_top = hist[tp] * ((s.empty() ? i : i - s.top() - 1) + 1);
 
            // update max area, if needed
            if (max_area < area_with_top)
                max_area = area_with_top;
        }
    }
 
    // Now pop the remaining bars from stack and calculate area with every
    // popped bar as the smallest bar
    while (s.empty() == false)
    {
        tp = s.top();
        s.pop();
        area_with_top = hist[tp] * ((s.empty() ? i : i - s.top() - 1) + 1);
 
        if (max_area < area_with_top)
            max_area = area_with_top;
    }
 
    return max_area;
}

int main()
{
  scanf("%d %d",&r,&c);
  int risan = max(r,c);
  REP(i,r) data[i] = GetString();
  REP(j,c-1) atas[0][j] = 1;
  FOR(i,1,r) REP(j,c-1)
  {
    bool samanow = data[i][j] == data[i][j+1];
    bool samaatas = data[i-1][j] == data[i-1][j+1];
    if (samanow == samaatas) atas[i][j] = atas[i-1][j] + 1;
    else atas[i][j] = 1;
  }
  // REP(i,r) 
  // {
  //     REP(j,c) debug("%d ",atas[i][j]);
  //     debug("\n");
  // }
  FOR(i,1,r)
  {
    REP(j,c-1) hist[j] = atas[i][j];
    MAX(risan,getMaxArea());
    // REP(j,c-1) VALUE(hist[j]);
    // VALUE(getMaxArea());
  }
  printf("%d\n",risan);
  return 0;
}










Measured memory_bytes: 19968