Buggy python submission (verdict: Runtime Error):
import numpy as np

N, M, K = map(int, input().split())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

# 累積和
A = np.cumsum(A)
B = np.cumsum(B)

# K以下を抽出
A = A[A <= K]
B = B[B <= K]

# Aを逆順にする
A = A[::-1]

c = 0
c_max = 0
for i, a in enumerate(A):
    c += len(A) - i

    for j, b in enumerate(B):
        if a + b <= K:
            cb = j + 1

    c += cb
    if c > c_max:
        c_max = c
    c = 0

print(c_max)


Fixed submission:
import numpy as np

from numba import njit


@njit("i8[:](i8, i8[:], i8[:])", cache=True)
def cumsum(K, A, cA):
    for i, a in enumerate(A):
        cA[i] += cA[i - 1] + A[i]
        if cA[i] > K:
            break

    cA = cA[cA != 0]
    cA = np.append(0, cA)
    return cA


@njit("i8(i8, i8[:], i8[:])", cache=True)
def solve(K, cA, cB):
    ans = np.searchsorted(cA, K - cB, side="right") - 1
    ans += np.arange(len(cB))
    return ans.max()


N, M, K = map(int, input().split())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

cA = np.zeros(N, dtype=np.int64)
cB = np.zeros(M, dtype=np.int64)

# np.cumsumだとoverflowする
cA = cumsum(K, A, cA)
cB = cumsum(K, B, cB)

ans = solve(K, cA, cB)
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
def SS(A, K):
    sA = 0
    AA = []
    for a in A:
        sA += a
        if sA > K:
            break
        AA.append(sA)

    return AA


def main():
    N, M, K = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))

    AA = SS(A, K)
    BB = SS(B, K)
    AA = AA[::-1]

    M = max(len(AA), len(BB))

    left = 0
    right = len(BB) - 1

    while left < len(AA):
        if AA[left] + BB[right] <= K:
            m = len(AA) - left + right + 1
            if m > M:
                M = m
            left += 1
            right = len(BB) - 1
        else:
            right -= 1
            if right < 0:
                left += 1
                right = len(BB) - 1

    print(M)


main()


Fixed submission:
import numpy as np

from numba import njit


@njit("i8[:](i8, i8[:], i8[:])", cache=True)
def cumsum(K, A, cA):
    for i, a in enumerate(A):
        cA[i] += cA[i - 1] + A[i]
        if cA[i] > K:
            break

    cA = cA[cA != 0]
    cA = np.append(0, cA)
    return cA


@njit("i8(i8, i8[:], i8[:])", cache=True)
def solve(K, cA, cB):
    ans = np.searchsorted(cA, K - cB, side="right") - 1
    ans += np.arange(len(cB))
    return ans.max()


N, M, K = map(int, input().split())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

cA = np.zeros(N, dtype=np.int64)
cB = np.zeros(M, dtype=np.int64)

# np.cumsumだとoverflowする
cA = cumsum(K, A, cA)
cB = cumsum(K, B, cB)

ans = solve(K, cA, cB)
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
def SS(A, K):
    sA = 0
    AA = []
    for a in A:
        sA += a
        if sA > K:
            break
        AA.append(sA)

    return AA


def main():
    N, M, K = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))

    AA = SS(A, K)
    BB = SS(B, K)
    AA = AA[::-1]

    M = max(len(AA), len(BB))

    left = 0
    right = len(BB) - 1

    while left < len(AA):
        if AA[left] + BB[right] <= K:
            m = len(AA) - left + right + 1
            if m > M:
                M = m
            left += 1
            right = len(BB) - 1
        else:
            right -= 1
            if right < 0:
                left += 1
                right = len(BB) - 1

    print(M)


main()


Fixed submission:
import numpy as np

from numba import njit


@njit("i8[:](i8, i8[:], i8[:])", cache=True)
def cumsum(K, A, cA):
    for i, a in enumerate(A):
        cA[i] += cA[i - 1] + A[i]
        if cA[i] > K:
            break

    cA = cA[cA != 0]
    cA = np.append(0, cA)
    return cA


@njit("i8(i8, i8[:], i8[:])", cache=True)
def solve(K, cA, cB):
    ans = np.searchsorted(cA, K - cB, side="right") - 1
    ans += np.arange(len(cB))
    return ans.max()


N, M, K = map(int, input().split())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

cA = np.zeros(N, dtype=np.int64)
cB = np.zeros(M, dtype=np.int64)

# np.cumsumだとoverflowする
cA = cumsum(K, A, cA)
cB = cumsum(K, B, cB)

ans = solve(K, cA, cB)
print(ans)

Buggy python submission (verdict: Runtime Error):
def main():
    N, M, K = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))

    sA = 0
    AA = []
    for a in A:
        sA += a
        if sA > K:
            break
        AA.append(sA)

    sB = 0
    BB = []
    for b in B:
        sB += b
        if sB > K:
            break
        BB.append(sB)

    AA = AA[::-1]

    M = max(len(AA), len(BB))

    for i in range(len(AA)):
        for j in range(len(BB)):
            if AA[i] + BB[i] <= K:
                m = len(AA) - i + j + 1
                if m > M:
                    M = m
    print(M)

main()


Fixed submission:
import numpy as np

from numba import njit


@njit("i8[:](i8, i8[:], i8[:])", cache=True)
def cumsum(K, A, cA):
    for i, a in enumerate(A):
        cA[i] += cA[i - 1] + A[i]
        if cA[i] > K:
            break

    cA = cA[cA != 0]
    cA = np.append(0, cA)
    return cA


@njit("i8(i8, i8[:], i8[:])", cache=True)
def solve(K, cA, cB):
    ans = np.searchsorted(cA, K - cB, side="right") - 1
    ans += np.arange(len(cB))
    return ans.max()


N, M, K = map(int, input().split())
A = np.array(input().split(), dtype=np.int64)
B = np.array(input().split(), dtype=np.int64)

cA = np.zeros(N, dtype=np.int64)
cB = np.zeros(M, dtype=np.int64)

# np.cumsumだとoverflowする
cA = cumsum(K, A, cA)
cB = cumsum(K, B, cB)

ans = solve(K, cA, cB)
print(ans)