# -*- coding: utf-8 -*-



import sys



def input(): return sys.stdin.readline().strip()

def list2d(a, b, c): return [[c] * b for i in range(a)]

def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]

def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]

def ceil(x, y=1): return int(-(-x // y))

def INT(): return int(eval(input()))

def MAP(): return list(map(int, input().split()))

def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]

def Yes(): print('Yes')

def No(): print('No')

def YES(): print('YES')

def NO(): print('NO')

sys.setrecursionlimit(10 ** 7)

INF = 10 ** 18

MOD = 10 ** 9 + 7



def bisearch_min(mn, mx, func):

    """ 条件を満たす最小値を見つける二分探索 """



    ok = mx

    ng = mn

    while ng+1 < ok:

        mid = (ok+ng) // 2

        if func(mid):

            # 下を探しに行く

            ok = mid

        else:

            # 上を探しに行く

            ng = mid

    return ok



N, K = MAP()

A = LIST()

B = LIST()



A.sort(reverse=True)

B.sort()



def check(m):

    k = 0

    for i, a in enumerate(A):

        b = B[i]

        k += max(ceil(a - m/b), 0)

        if k > K:

            return False

    return True



print((bisearch_min(-1, INF, check)))

# -*- coding: utf-8 -*-



import sys



def input(): return sys.stdin.readline().strip()

def list2d(a, b, c): return [[c] * b for i in range(a)]

def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]

def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]

def ceil(x, y=1): return int(-(-x // y))

def INT(): return int(eval(input()))

def MAP(): return list(map(int, input().split()))

def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]

def Yes(): print('Yes')

def No(): print('No')

def YES(): print('YES')

def NO(): print('NO')

sys.setrecursionlimit(10 ** 7)

INF = 10 ** 18

MOD = 10 ** 9 + 7



def bisearch_min(mn, mx, func):

    """ 条件を満たす最小値を見つける二分探索 """



    ok = mx

    ng = mn

    while ng+1 < ok:

        mid = (ok+ng) // 2

        if func(mid):

            # 下を探しに行く

            ok = mid

        else:

            # 上を探しに行く

            ng = mid

    return ok



N, K = MAP()

A = LIST()

B = LIST()



A.sort(reverse=True)

B.sort()



def check(m):

    k = 0

    for i, a in enumerate(A):

        b = B[i]

        k += max(ceil(a - m/b), 0)

        if k > K:

            return False

    return True



print((bisearch_min(-1, 10**12, check)))

# -*- coding: utf-8 -*-
import sys


def input():
    return sys.stdin.readline().strip()


def list2d(a, b, c):
    return [[c] * b for i in range(a)]


def list3d(a, b, c, d):
    return [[[d] * c for j in range(b)] for i in range(a)]


def list4d(a, b, c, d, e):
    return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]


def ceil(x, y=1):
    return int(-(-x // y))


def INT():
    return int(eval(input()))


def MAP():
    return list(map(int, input().split()))


def LIST(N=None):
    return list(MAP()) if N is None else [INT() for i in range(N)]


def Yes():
    print("Yes")


def No():
    print("No")


def YES():
    print("YES")


def NO():
    print("NO")


sys.setrecursionlimit(10**7)
INF = 10**18
MOD = 10**9 + 7


def bisearch_min(mn, mx, func):
    """条件を満たす最小値を見つける二分探索"""
    ok = mx
    ng = mn
    while ng + 1 < ok:
        mid = (ok + ng) // 2
        if func(mid):
            # 下を探しに行く
            ok = mid
        else:
            # 上を探しに行く
            ng = mid
    return ok


N, K = MAP()
A = LIST()
B = LIST()
A.sort(reverse=True)
B.sort()


def check(m):
    k = 0
    for i, a in enumerate(A):
        b = B[i]
        k += max(ceil(a - m / b), 0)
        if k > K:
            return False
    return True


print((bisearch_min(-1, INF, check)))

# -*- coding: utf-8 -*-
import sys


def input():
    return sys.stdin.readline().strip()


def list2d(a, b, c):
    return [[c] * b for i in range(a)]


def list3d(a, b, c, d):
    return [[[d] * c for j in range(b)] for i in range(a)]


def list4d(a, b, c, d, e):
    return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]


def ceil(x, y=1):
    return int(-(-x // y))


def INT():
    return int(eval(input()))


def MAP():
    return list(map(int, input().split()))


def LIST(N=None):
    return list(MAP()) if N is None else [INT() for i in range(N)]


def Yes():
    print("Yes")


def No():
    print("No")


def YES():
    print("YES")


def NO():
    print("NO")


sys.setrecursionlimit(10**7)
INF = 10**18
MOD = 10**9 + 7


def bisearch_min(mn, mx, func):
    """条件を満たす最小値を見つける二分探索"""
    ok = mx
    ng = mn
    while ng + 1 < ok:
        mid = (ok + ng) // 2
        if func(mid):
            # 下を探しに行く
            ok = mid
        else:
            # 上を探しに行く
            ng = mid
    return ok


N, K = MAP()
A = LIST()
B = LIST()
A.sort(reverse=True)
B.sort()


def check(m):
    k = 0
    for i, a in enumerate(A):
        b = B[i]
        k += max(ceil(a - m / b), 0)
        if k > K:
            return False
    return True


print((bisearch_min(-1, 10**12, check)))

-print((bisearch_min(-1, INF, check))) +print((bisearch_min(-1, 10**12, check)))