R=range
J=lambda:list(map(int,input().split()))
N,M=J()
A=[[0]*(M+1)for c in R(11)]
z=0
for C,D in reversed(sorted(J()for i in R(N))):
	if C<1:z+=D;continue
	for c in R(9,-1,-1):
		k=C<<c
		for j in R(M-k+1):A[c+1][j]=max(A[c+1][j],A[c][j+k]+D)
print(max(max(a)for a in A)+z)