N, M = map(int, input().split())
dp = [-1 for _ in range(M + 1)]
dp[0] = 0
ans = 0
X = []
for i in range(N):
  C, D = map(int, input().split())
  if C == 0: ans += D
  else: X.append((C, D))
X.sort()
res = 0
for c, d in X:
  for m in range(M, -1, -1):
    e = dp[m]
    if e == -1:
      continue
    if 2 * m + c <= M:
      dp[2 * m + c] = max(dp[2 * m + c], e + d)
  res = max(res, max(dp))
ans += res
print(ans)