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

constexpr int maxn = 1010;

int v[maxn][maxn], h[maxn] = {}, st[maxn], dr[maxn], stiva[maxn] = {}, poz = -1,
    n, m;
ifstream f("hambar.in");
ofstream g("hambar.out");

void do_st_dr(){
    stiva[poz=0] = -1;
    for(int i = 0; i < n; ++i){
        while(stiva[poz] != -1 && h[stiva[poz]] >= h[i]) --poz;
        st[i] = stiva[poz]+1;
        stiva[++poz] = i; }
    stiva[poz=0] = n;
    for(int i = n-1; i >= 0; --i){
        while(stiva[poz] != n && h[stiva[poz]] >= h[i]) --poz;
        dr[i] = stiva[poz]-1;
        stiva[++poz] = i; } }

int main(){
    f >> n >> m;
    for(int i = 0, x, y; i < m; ++i)
        f >> x >> y,
        v[x-1][y-1] = 1;

    int rez = 0;
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j)
            if(!v[i][j]) ++h[j];
            else h[j] = 0;
        do_st_dr();
/**        for(int j = 0; j < n; ++j) cout << h[j] << ' ';
        cout << endl;

        for(int j = 0; j < n; ++j) cout << st[j] << ' ';
        cout << endl;

        for(int j = 0; j < n; ++j) cout << dr[j] << ' ';
        cout << endl;
        cout << endl;
        **/
        for(int j = 0; j < n; ++j)
            rez = max(rez, h[j] * (dr[j] - st[j] + 1)); }
    g << rez << endl;
    return 0; }