Buggy python submission (verdict: Runtime Error):
# 2020/05/02
# AtCoder Beginner Contest 165 - C

a = list()
def mkArray(in_list, sav_val, cnt):
    if cnt >= m:
        a.append(in_list)
        return 0
    else:
        for x in range(sav_val, m + 1):
            wk_list = list()
            wk_list.extend(in_list)
            wk_list.append(x)
            mkArray(wk_list, x, cnt + 1)

# Input
n, m, q = map(int,input().split())
abcd = list()

for i in range(q):
    w_abcd = list(map(int,input().split()))
    abcd.append(w_abcd)

# Make Array
w_a = list()
mkArray(w_a, 1, 0)

# Search
ans = 0
for i in range(len(a)):
    wans = 0
    for j in range(q):
        if a[i][abcd[j][1]-1] - a[i][abcd[j][0]-1] == abcd[j][2]:
            wans = wans + abcd[j][3]

    if wans > ans:
        ans = wans

# Output
print(ans)


Fixed submission:
# 2020/05/02
# AtCoder Beginner Contest 165 - C

a = list()
def mkArray(in_list, sav_val, cnt):
    if cnt >= n:
        a.append(in_list)
        return 0
    else:
        for x in range(sav_val, m + 1):
            wk_list = list()
            wk_list.extend(in_list)
            wk_list.append(x)
            mkArray(wk_list, x, cnt + 1)

# Input
n, m, q = map(int,input().split())
abcd = list()

for i in range(q):
    w_abcd = list(map(int,input().split()))
    abcd.append(w_abcd)

# Make Array
w_a = list()
mkArray(w_a, 1, 0)

# Search
ans = 0
for i in range(len(a)):
    wans = 0
    for j in range(q):
        if a[i][abcd[j][1]-1] - a[i][abcd[j][0]-1] == abcd[j][2]:
            wans = wans + abcd[j][3]

    if wans > ans:
        ans = wans

# Output
print(ans)

Buggy python submission (verdict: Runtime Error):
# 2020/05/02
# AtCoder Beginner Contest 165 - C

a = list()
def mkArray(in_list, sav_val, cnt):
    if cnt >= m - 1:
        a.append(in_list)
        return 0
    else:
        for x in range(sav_val, m + 1):
            wk_list = list()
            wk_list.extend(in_list)
            wk_list.append(x)
            mkArray(wk_list, x, cnt + 1)

# Input
n, m, q = map(int,input().split())
abcd = list()

for i in range(q):
    w_abcd = list(map(int,input().split()))
    abcd.append(w_abcd)

# Make Array
w_a = list()
mkArray(w_a, 1, 0)

# Search
ans = 0
for i in range(len(a)):
    wans = 0
    for j in range(q):
        if a[i][abcd[j][1]-1] - a[i][abcd[j][0]-1] == abcd[j][2]:
            wans = wans + abcd[j][3]

    if wans > ans:
        ans = wans

# Output
print(ans)


Fixed submission:
# 2020/05/02
# AtCoder Beginner Contest 165 - C

a = list()
def mkArray(in_list, sav_val, cnt):
    if cnt >= n:
        a.append(in_list)
        return 0
    else:
        for x in range(sav_val, m + 1):
            wk_list = list()
            wk_list.extend(in_list)
            wk_list.append(x)
            mkArray(wk_list, x, cnt + 1)

# Input
n, m, q = map(int,input().split())
abcd = list()

for i in range(q):
    w_abcd = list(map(int,input().split()))
    abcd.append(w_abcd)

# Make Array
w_a = list()
mkArray(w_a, 1, 0)

# Search
ans = 0
for i in range(len(a)):
    wans = 0
    for j in range(q):
        if a[i][abcd[j][1]-1] - a[i][abcd[j][0]-1] == abcd[j][2]:
            wans = wans + abcd[j][3]

    if wans > ans:
        ans = wans

# Output
print(ans)