N,M=map(int,input().split())
dp=[[-10**10]*(M+1) for k in range(12)]
dp[0][0]=0
np=[[-10**10]*(M+1) for k in range(12)]
L=[]
for i in range(N):
  c,d=map(int,input().split())
  L.append((c,d))
L.sort(reverse=True)
p=[1]*12
for k in range(12):
  p[k]=2**k
for i in range(N):
  a,b=L[i][:]
  for x in range(M+1):
    for k in range(12):
      if dp[k][x]<0:
        continue
      if x+a*p[k]>M:
        continue
      np[min(k+1,11)][x+a*p[k]]=max(np[k+1][x+a*p[k]],dp[k][x]+b)
  for x in range(M+1):
    for k in range(12):
      dp[k][x]=max(dp[k][x],np[k][x])
result=0
for k in range(12):
  result=max(result,max(dp[k]))
print(result)