Buggy python submission (verdict: Runtime Error):
from itertools import product
from collections import Counter
 
n, c = map(int, input().split())
color_costs = [list(map(int, input().split())) for _ in range(c)]
matrix = [list(map(int, input().split())) for _ in range(n)]
 
colord = {(i, j):cost for i, row in enumerate(color_costs)
                      for j, cost in enumerate(row)}
 
res = []
for n in range(3):
  color_count = Counter(c-1 for i, row in enumerate(matrix) 
                            for j, c in enumerate(row) 
                            if (i + j) % 3 == n)
  def color_cost(color):
    return sum(colord[ccolor, color] * ccount for ccolor, ccount in color_count.items())
  cx = [(color, color_cost(color)) for color in range(c)]
  sorted_by_cost = sorted(cx, key=lambda x:x[1])
  cheapest3 = sorted_by_cost[:3]
  res.append(cheapest3)
 
color_pickss = product(*res)
filtered_unique = (picks for picks in color_pickss if len(set(x[0] for x in picks)) == 3)
costs = (sum(x[1] for x in picks) for pick in filtered_unique)
print(min(costs))
from itertools import product
from collections import Counter
 
n, c = map(int, input().split())
color_costs = [list(map(int, input().split())) for _ in range(c)]
matrix = [list(map(int, input().split())) for _ in range(n)]

colord = {(i, j):cost for i, row in enumerate(color_costs)
                      for j, cost in enumerate(row)}
 
res = []
for n in range(3):
  color_count = Counter(c-1 for i, row in enumerate(matrix) 
                            for j, c in enumerate(row) 
                            if (i + j) % 3 == n)
  def color_cost(color):
    return sum(colord[ccolor, color] * ccount for ccolor, ccount in color_count.items())
  cx = [(color, color_cost(color)) for color in range(c)]
  sorted_by_cost = sorted(cx, key=lambda x:x[1])
  cheapest3 = sorted_by_cost[:3]
  res.append(cheapest3)

color_pickss = product(*res)
filtered_unique = (picks for picks in color_pickss if len(set(x[0] for x in picks)) == 3)
costs = (sum(x[1] for x in picks) for picks in filtered_unique)
print(min(costs))

Fixed submission:
from itertools import product
n, c = map(int, input().split())
color_costs = [map(int, input().split()) for _ in range(c)]
matrix = [map(int, input().split()) for _ in range(n)]
colord = {(i+1, j+1):cost for i, row in enumerate(color_costs)
                         for j, cost in enumerate(row)}
 
cellgroups = [[] for _ in range(3)]
for i, row in enumerate(matrix):
  for j, color in enumerate(row):
    cellgroups[(i+1+j+1)%3].append(color)
  
cc = [[(color, sum(colord[cellcolor, color] for cellcolor in cells))
	       									for color in range(1,c+1)]
      										for cells in cellgroups]
 
dd = [sorted(xs, key=lambda x:x[1])[:3] for xs in cc]
ee = (a[1]+b[1]+c[1] for a, b, c in product(*dd) if len(set((a[0], b[0], c[0]))) == 3)
print(min(ee))

Buggy python submission (verdict: Runtime Error):
from itertools import product
from collections import Counter
 
n, c = map(int, input().split())
color_costs = [list(map(int, input().split())) for _ in range(c)]
matrix = [list(map(int, input().split())) for _ in range(n)]

colord = {(i, j):cost for i, row in enumerate(color_costs)
                      for j, cost in enumerate(row)}
 
res = []
for n in range(3):
  color_count = Counter(c-1 for i, row in enumerate(matrix) 
                            for j, c in enumerate(row) 
                            if (i + j) % 3 == n)
  def color_cost(color):
    return sum(colord[ccolor, color] * ccount for ccolor, ccount in color_count.items())
  cx = [(color, color_cost(color)) for color in range(c)]
  sorted_by_cost = sorted(cx, key=lambda x:x[1])
  cheapest3 = sorted_by_cost[:3]
  res.append(cheapest3)

color_pickss = product(*res)
filtered_unique = (picks for picks in color_pickss if len(set(x[0] for x in picks)) == 3)
costs = (sum(x[1] for x in picks) for pick in filtered_unique)
print(min(costs))

Fixed submission:
from itertools import product
n, c = map(int, input().split())
color_costs = [map(int, input().split()) for _ in range(c)]
matrix = [map(int, input().split()) for _ in range(n)]
colord = {(i+1, j+1):cost for i, row in enumerate(color_costs)
                         for j, cost in enumerate(row)}
 
cellgroups = [[] for _ in range(3)]
for i, row in enumerate(matrix):
  for j, color in enumerate(row):
    cellgroups[(i+1+j+1)%3].append(color)
  
cc = [[(color, sum(colord[cellcolor, color] for cellcolor in cells))
	       									for color in range(1,c+1)]
      										for cells in cellgroups]
 
dd = [sorted(xs, key=lambda x:x[1])[:3] for xs in cc]
ee = (a[1]+b[1]+c[1] for a, b, c in product(*dd) if len(set((a[0], b[0], c[0]))) == 3)
print(min(ee))