#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <chrono>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


int N, M;
vector<pair<int, Int>> P;

int main() {
  for (; ~scanf("%d%d", &N, &M); ) {
    P.resize(N);
    for (int i = 0; i < N; ++i) {
      scanf("%d%lld", &P[i].first, &P[i].second);
    }
    sort(P.begin(), P.end());
    
    vector<Int> dp(M + 1, 0);
    for (int i = 0; i < N; ++i) {
      for (int m = M; m >= P[i].first; --m) {
        chmax(dp[m], P[i].second + dp[(m - P[i].first) >> 1]);
      }
    }
//cerr<<"dp = "<<dp<<endl;
    printf("%lld\n", dp[M]);
  }
  return 0;
}