# conver the following C++ code into pypy3
#https://yukicoder.me/submissions/1041891


from collections import deque

def main():
    N, M = map(int, input().split())
    hand = []
    
    for _ in range(N):
        C, D = map(int, input().split())
        hand.append((C, D))
    
    # Sort the hand by the first value in descending order
    hand.sort(reverse=True, key=lambda x: (x[0], x[1]))

    dp = [0] * (M + 1)
    dp[M] = 0

    for C, D in hand:
        for i in range(C, M + 1):
            dp[(i - C) // 2] = max(dp[(i - C) // 2], dp[i] + D)

    ans = max(dp)
    print(ans)

if __name__ == "__main__":
    main()