N,M=map(int,input().split())
dp=[0]*(M+1)
np=[0]*(M+1)
L=[]
p=0
for i in range(N):
  c,d=map(int,input().split())
  if c==0:
    p+=d
  else:
    L.append((c,d))
L.sort()
N=len(L)
result=0
for i in range(N):
  a,b=L[i][:]
  for x in range(a,M+1):
    np[x]=max(dp[x-a]+b,np[x])
  for x in range(a):
    np[x]=max(np[x],dp[x])
  w=max(np)
  result=max(result,w)
  for x in range(M+1):
    if x%2==0:
      dp[x]=np[x//2]
    else:
      dp[x]=0
print(result+p)