Buggy python submission (verdict: Time Limit Exceeded):
import math,itertools,fractions,heapq,collections,bisect,sys,queue,copy

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7
dd=[(-1,0),(0,1),(1,0),(0,-1)]
ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return input()

n=0
m=0
ans=-inf
l=[]

def dfs(s):
  global n
  global m
  global ans
  global l

  if len(s)==n:
    _ans=0
    for a,b,c,d in l:
      a-=1
      b-=1
      if int(s[b])-int(s[a])==c:
        _ans+=d
    ans=max(ans,_ans)

  if len(s)!=n:
    x=int(s[-1])
    for i in range(x,m+1):
      dfs(s+str(i))

def main():
  global n
  global m
  global ans
  global l

  n,m,q=LI()
  l=[LI() for _ in range(q)]

  for i in range(1,m+1):
    dfs(str(i))

  return ans

# main()
print(main())


Fixed submission:
import math,itertools,fractions,heapq,collections,bisect,sys,queue,copy

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7
dd=[(-1,0),(0,1),(1,0),(0,-1)]
ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return input()

n=0
m=0
ans=-inf
l=[]

def dfs(s):
  global n
  global m
  global ans
  global l

  if len(s)==n:
    _ans=0
    for a,b,c,d in l:
      a-=1
      b-=1
      if s[b]-s[a]==c:
        _ans+=d
    ans=max(ans,_ans)

  if len(s)!=n:
    x=s[-1]
    for i in range(x,m+1):
      dfs(s+[i])

def main():
  global n
  global m
  global ans
  global l

  n,m,q=LI()
  l=[LI() for _ in range(q)]

  for i in range(1,m+1):
    dfs([i])

  return ans

# main()
print(main())

Buggy python submission (verdict: Runtime Error):
import math,itertools,fractions,heapq,collections,bisect,sys,queue,copy

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7
dd=[(-1,0),(0,1),(1,0),(0,-1)]
ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return input()

def main():
  n,m,q=LI()
  l=[False]*n
  ans=0

  ll=[]
  for _ in range(q):
    _l=LI()
    ll.append(_l)

  for i in range(1<<n):
    l=[False]*n
    _ans=0
    for j in range(n):
      if i&(1<<j):
        a,b,c,d=ll[j]
        a-=1
        b-=1
        if l[a] and l[b]:
          continue
        l[a]=True
        l[b]=True
        _ans+=d
    ans=max(ans,_ans)
  return ans

# main()
print(main())


Fixed submission:
import math,itertools,fractions,heapq,collections,bisect,sys,queue,copy

sys.setrecursionlimit(10**7)
inf=10**20
mod=10**9+7
dd=[(-1,0),(0,1),(1,0),(0,-1)]
ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return input()

n=0
m=0
ans=-inf
l=[]

def dfs(s):
  global n
  global m
  global ans
  global l

  if len(s)==n:
    _ans=0
    for a,b,c,d in l:
      a-=1
      b-=1
      if s[b]-s[a]==c:
        _ans+=d
    ans=max(ans,_ans)

  if len(s)!=n:
    x=s[-1]
    for i in range(x,m+1):
      dfs(s+[i])

def main():
  global n
  global m
  global ans
  global l

  n,m,q=LI()
  l=[LI() for _ in range(q)]

  for i in range(1,m+1):
    dfs([i])

  return ans

# main()
print(main())