import sys
input = sys.stdin.readline

from operator import itemgetter

N,M=map(int,input().split())

POW2=[1]
for i in range(50):
    POW2.append(POW2[-1]*2)

CD=[list(map(int,input().split())) for i in range(N)]

CD.sort(key=itemgetter(0),reverse=True)

DP=[[0]*(M+1) for i in range(30)]

for x,y in CD:
    for i in range(29,-1,-1):
        for j in range(M+1):
            if x==0:
                DP[i][j]+=y
            else:
                if j-POW2[i]*x>=0:
                    DP[i+1][j-POW2[i]*x]=max(DP[i+1][j-POW2[i]*x],DP[i][j]+y)

ANS=0

for i in range(30):
    ANS=max(ANS,max(DP[i]))

print(ANS)