from sys import stdin
input = stdin.readline

INF = 1<<60

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

CD.sort(key=lambda x:x[0])
dp = [-INF]*(M+1)
dp[0] = 0
ndp = [-INF]*(M+1)
for C, D in CD:
    for i in range(M+1): ndp[i] = -INF
    for i in range(M+1):
        if dp[i] == -INF: continue
        ndp[i] = max(ndp[i], dp[i])
        if i*2+C <= M:
            ndp[i*2+C] = max(ndp[i*2+C], dp[i]+D)
    dp, ndp = ndp, dp

print(max(dp))