import java.util.BitSet;

class Xor128 {
  public static final int RAND_INF = 10000000;
  private int x = 123456789, y = 362436069, z = 521288629, w = 88675123;

  public int next(int max) {
    return next() % max;
  }

  public int next() {
    int t = (x ^ (x << 11));
    x = y;
    y = z;
    z = w;
    return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
  }

  public void shuffle(int[] array) {
    int n = array.length;
    for (int i = n - 1; i >= 1; i--) {
      int j = next() % i;
      int tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }
}

class State {
  public BitSet set;
  public long score = 0;
  public long w = 0;

  public State(int n) {
    this.set = new BitSet(n);
  }
  
  public State(State state) {
    this.set = new BitSet(state.set.length());
    this.score = state.score;
    this.w = state.w;
  }
}

public class Main {
  private static final long TIME = 1900;
  private static final int R = 1000;

  private static void solve() {
    int N = ni();
    long W = nl();
    long[][] item = new long[N][3];
    for (int i = 0; i < N; i ++) {
      item[i][0] = i;
      item[i][1] = nl();
      item[i][2] = nl();
    }
    
    Xor128 rand = new Xor128();
    long start = System.currentTimeMillis();
    long now = System.currentTimeMillis();
    
    int count = 0;

    State state = new State(N);
    State bestState = new State(state);

    while (now - start <= TIME) {
      count ++;
      if (count % 100 == 0) {
        now = System.currentTimeMillis();
      }
      long time = now - start;

      int idx = rand.next(N);
      long nextW = 0;
      long nextScore = 0;

      if (state.set.get(idx)) {
        nextW = state.w - item[idx][2];
        nextScore = state.score - item[idx][1];
      } else {
        nextW = state.w + item[idx][2];
        nextScore = nextW > W ? -1 : state.score + item[idx][1];
      }
      
      boolean forceNext = R * (TIME - time) > TIME * (rand.next(R));
      if (nextScore > state.score || (forceNext && nextScore >= 0)) {
        state.set.flip(idx);
        state.w = nextW;
        state.score = nextScore;
      }
      
      if (state.score > bestState.score) {
        bestState = new State(state);
      }
    }
    //System.err.println(now - start + "ms");
    System.out.println(bestState.score);
  }

  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}