Buggy python submission (verdict: Time Limit Exceeded):
from itertools import permutations

N, C = list(map(int, input().split()))
D =[list(map(int, input().split())) for _ in range(C)] 

remains = {0: [], 1: [], 2: []} 
for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3].append(line[j])

INF = 65535

def recolor(x, y): 
    return D[x-1][y-1]

answer = INF 
for choice in permutations(range(1, C+1), 3): 
    _answer = 0 
    for i, c in enumerate(choice):
        _answer += sum([recolor(r, c) for r in remains[i] if c != r]) 
    answer = min(answer, _answer)

print(answer)

Fixed submission:
from itertools import permutations
from collections import defaultdict

N, C = list(map(int, input().split()))
D =[list(map(int, input().split())) for _ in range(C)]

remains = {0: defaultdict(int), 1: defaultdict(int), 2: defaultdict(int)}
for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3][line[j]] += 1

INF = float('inf')

def recolor(x, y, count):
    return D[x-1][y-1] * count

answer = INF
for choice in permutations(range(1, C+1), 3):
    _answer = 0
    for i, c in enumerate(choice):
        _answer += sum([recolor(r, c, remains[i][r]) for r in remains[i] if c != r])
    answer = min(answer, _answer)

print(answer)

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import permutations

N, C = list(map(int, input().split()))

D = []
for i in range(C):
    D.append(list(map(int, input().split())))

remains = {0: [], 1: [], 2: []}

for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3].append(line[j])

INF = 65535

def recolor(x, y):
    return D[x-1][y-1]

memo = {0: {}, 1: {}, 2: {}}

answer = INF
for choice in permutations(list(range(1, C+1)), 3):
    _answer = 0
    for i in range(3):
        total = memo[i].get(
            choice[i],
            sum([recolor(r, choice[i]) for r in remains[i] if choice[i] != r])
        ) 
        memo[i][choice[i]] = total
        _answer += total 
    answer = min(answer, _answer)

print(answer)

Fixed submission:
from itertools import permutations
from collections import defaultdict

N, C = list(map(int, input().split()))
D =[list(map(int, input().split())) for _ in range(C)]

remains = {0: defaultdict(int), 1: defaultdict(int), 2: defaultdict(int)}
for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3][line[j]] += 1

INF = float('inf')

def recolor(x, y, count):
    return D[x-1][y-1] * count

answer = INF
for choice in permutations(range(1, C+1), 3):
    _answer = 0
    for i, c in enumerate(choice):
        _answer += sum([recolor(r, c, remains[i][r]) for r in remains[i] if c != r])
    answer = min(answer, _answer)

print(answer)

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import permutations

N, C = list(map(int, input().split()))

D = []
for i in range(C):
    D.append(list(map(int, input().split())))

remains = {0: [], 1: [], 2: []}

for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3].append(line[j])

INF = 65535

def recolor(x, y):
    return D[x-1][y-1]

answer = INF
for choice in permutations(list(range(1, C+1)), 3):
    _answer = 0
    for i in range(3):
        _answer += sum([recolor(r, choice[i]) for r in remains[i] if choice[i] != r])
    answer = min(answer, _answer)

print(answer)

Fixed submission:
from itertools import permutations
from collections import defaultdict

N, C = list(map(int, input().split()))
D =[list(map(int, input().split())) for _ in range(C)]

remains = {0: defaultdict(int), 1: defaultdict(int), 2: defaultdict(int)}
for i in range(1, N+1):
    line = list(map(int, input().split()))
    for j in range(N):
        remains[(i+j+1)%3][line[j]] += 1

INF = float('inf')

def recolor(x, y, count):
    return D[x-1][y-1] * count

answer = INF
for choice in permutations(range(1, C+1), 3):
    _answer = 0
    for i, c in enumerate(choice):
        _answer += sum([recolor(r, c, remains[i][r]) for r in remains[i] if c != r])
    answer = min(answer, _answer)

print(answer)