#include <iostream>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <cstring>
#include <vector>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <ctime>
using namespace std;

#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define rep(i,n) FOR(i,0,n)
#define RFOR(i,b,a) for (int i = (b)-1; i >= (a); i--)
#define ITER(it,a) for (__typeof(a.begin()) it = a.begin(); it != a.end(); it++)
#define FILL(a,value) memset(a, value, sizeof(a))

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL>VL;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;

const double PI = acos(-1.0);
const int INF = 1000 * 1000 * 1000 + 7;
const LL LINF = LL(1e18);
const LL MAS = 1e6;
const double EPS = 1e-7;
const LL MAX = 4294967296;

int main()
{
   int n,m;
   cin >> n >> m;
   vector < vector<LL > >   g(m) ;
   vector <vector < LL > > g1(m ) ;
   rep(i,n)
   {
       int x,y;
       cin >> x >> y ;
       --x ;
       g1[x].PB(y);
   }
   rep(i,m)
   {
       sort(g1[i].begin(),g1[i].end()) ;
       reverse(g1[i].begin(),g1[i].end());

   }
   rep(i,m)
   {
       LL sum = 0;
       rep(j,g1[i].size())
       {
           sum+=g1[i][j];
           g[i].PB(sum) ;
       }
   }
  LL mxcount = 0;
   rep(j,m )
   {
       LL v  =g[j].size() ;
      mxcount = max(v,mxcount) ;
   }
   LL cur = 0;
   LL mx = 0 ;
   rep(j,mxcount)
   {
   rep(i,m )
   {
      if ( g[i].size() >= j+1)
      {
         cur+=g[i][j] ;
      }
   }
   mx =max(mx,cur) ;
   cur  = 0;
   }
   cout << mx ;

}