#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const ll INF = 1e18;
void chmax(ll &a, ll b) { a = max(a, b); }
void solve() {
  ll n, m;
  cin >> n >> m;
  vector<pair<ll, ll>> cds(n);
  rep(i, n) cin >> cds[i].first >> cds[i].second;
  sort(cds.rbegin(), cds.rend());
  vector<ll> dp(m + 1, -INF);
  dp[m] = 0;
  ll ans = 0;
  for (const auto [c, d] : cds) {
    for (ll j = c; j <= m; j++) {
      chmax(dp[(j - c) / 2], dp[j] + d);
      chmax(ans, dp[(j - c) / 2]);
    }
  }
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}