## https://yukicoder.me/problems/no/3077

MIN = -1

def main():
    N, M = map(int, input().split())
    cd = []
    for _ in range(N):
        c, d = map(int, input().split())
        cd.append((c, d))
    
    cd.sort(key=lambda x : x[0])

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

    for c, d in cd:
        l = M - c
        l //= 2
        for m in reversed(range(l + 1)):
            if dp[m] != MIN:
                w = 2 * m + c
                dp[w] = max(dp[w], dp[m] + d)
    
    print(max(dp))


                




if __name__ == "__main__":
    main()