/* -*- coding: utf-8 -*-
 *
 * 3077.cc:  No.3077 Goodstuff Deck Builder(Hard) - yukicoder
 */

#include<cstdio>
#include<algorithm>
#include<functional>
#include<utility>

using namespace std;

/* constant */

const int MAX_N = 10000;
const int MAX_M = 10000000;

/* typedef */

using ll = long long;
using pii = pair<int,int>;

/* global variables */

pii ps[MAX_N];
ll dp[MAX_M + 1];

/* subroutines */

void setmax(ll &a, ll b) { if (a < b) a = b; }

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);

  ll s0 = 0;
  int k = 0;
  for (int i = 0; i < n; i++) {
    int ci, di;
    scanf("%d%d", &ci, &di);
    if (ci == 0) s0 += di;
    else ps[k++] = {ci, di};
  }
  sort(ps, ps + k, greater<pii>());
  n = k;

  fill(dp, dp + m + 1, -1);
  dp[m] = 0;
  int cur = 0, nxt = 1;

  for (int i = 0; i < n; i++) {
    auto [ci, di] = ps[i];
    for (int j = ci; j <= m; j++)
      if (dp[j] >= 0)
	setmax(dp[(j - ci) / 2], dp[j] + di);
  }

  ll maxd = *max_element(dp, dp + m + 1);

  printf("%lld\n", s0 + maxd);

  return 0;
}