import sys
input = sys.stdin.readline

from operator import itemgetter

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

M0=M

X.sort(reverse=True)
X.sort(key=lambda x:x[0]/x[1],reverse=True)

ANS=0
LASTS=[]
for i in range(len(X)):
    v,w=X[i]
    if w<=M:
        ANS+=v
        M-=w
        LASTS.append((i,ANS,M))

if len(LASTS)<80:
    Q=[(0,0)]
    first=-1
    ANS=0
    M=M0
else:
    first,ANS,M=LASTS[-80]
    Q=[(0,0)]
    
for i in range(first+1,len(X)):
    v,w=X[i]
    NQ=[]
    for x,y in Q:
        if w+y<=M:
            NQ.append((v+x,w+y))

    Q+=NQ

    Q.sort(key=itemgetter(1))

    Q2=[]
    for x,y in Q:
        if Q2 and Q2[-1][0]>=x:
            continue
        else:
            Q2.append((x,y))
    Q=Q2
        

MAX=0
for x,y in Q:
    MAX=max(MAX,x)

print(ANS+MAX)