n, m = map(int, input().split())
CD = [list(map(int, input().split())) for _ in range(n)]
CD.sort(key=lambda x: -x[0])

dp = [0] * (m + 1)
for c, d in CD:
    for i in range(c, m + 1):
        dp[(i - c) // 2] = max(dp[(i - c) // 2], dp[i] + d)

print(dp[0])