N, M = map(int, input().split())
CD = sorted([list(map(int, input().split())) for _ in range(N)], key=lambda x:x[0], reverse=True)

INF = 1<<60

dp = [[-INF]*(M+1) for _ in range(11)]
dp[0][0] = 0
for C, D in CD:
    ndp = [[-INF]*(M+1) for _ in range(11)]
    for i in range(11):
        for j in range(M+1):
            if dp[i][j] == -INF:
                continue
            ndp[i][j] = max(ndp[i][j], dp[i][j])
            if j+C*2**i <= M:
                ndp[i+1][j+C*2**i] = max(ndp[i+1][j+C*2**i], dp[i][j]+D)
    dp = ndp

print(max(max(d) for d in dp))