Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

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

mod_0=defaultdict(int)
mod_1=defaultdict(int)
mod_2=defaultdict(int)

for i in range(N):
    for j in range(N):
        n=(i+j+2)%3
        if n==0:
            mod_0[grid[i][j]]+=1
        elif n==1:
            mod_1[grid[i][j]]+=1
        else:
            mod_2[grid[i][j]]+=1

ans=float("inf")
for i in range(C):
    for j in range(C):
        if i==j:
            continue
        for k in range(C):
            if k in [i,j]:
                continue

            total
            for prev,cnt in mod_0.items():
                total+=D[prev-1][i]*cnt
            for prev,cnt in mod_1.items():
                total+=D[prev-1][j]*cnt
            for prev,cnt in mod_2.items():
                total+=D[prev-1][k]*cnt
            
            ans=min(ans,total)
print(ans)

Fixed submission:
from collections import defaultdict

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

mod_0=defaultdict(int)
mod_1=defaultdict(int)
mod_2=defaultdict(int)

for i in range(N):
    for j in range(N):
        n=(i+j+2)%3
        if n==0:
            mod_0[grid[i][j]]+=1
        elif n==1:
            mod_1[grid[i][j]]+=1
        else:
            mod_2[grid[i][j]]+=1

ans=float("inf")
for i in range(C):
    for j in range(C):
        if i==j:
            continue
        for k in range(C):
            if k in [i,j]:
                continue

            total=0
            for prev,cnt in mod_0.items():
                total+=D[prev-1][i]*cnt
            for prev,cnt in mod_1.items():
                total+=D[prev-1][j]*cnt
            for prev,cnt in mod_2.items():
                total+=D[prev-1][k]*cnt
            
            ans=min(ans,total)
print(ans)

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

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

M=[[] for _ in range(3)]
for i in range(N):
    for j in range(N):
        n=(i+j+2)%3
        M[n].append(c[i][j])

ans=float("inf")
num=[i for i in range(1,C+1)]
for n,m,l in itertools.permutations(num,3):
    n,m,l=int(n),int(m),int(l)
    val=0
    for i in M[0]:
        val+=D[i-1][n-1]
    for j in M[1]:
        val+=D[j-1][m-1]
    for k in M[2]:
        val+=D[k-1][l-1]
    ans=min(ans,val)
print(ans)

Fixed submission:
from collections import defaultdict

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

mod_0=defaultdict(int)
mod_1=defaultdict(int)
mod_2=defaultdict(int)

for i in range(N):
    for j in range(N):
        n=(i+j+2)%3
        if n==0:
            mod_0[grid[i][j]]+=1
        elif n==1:
            mod_1[grid[i][j]]+=1
        else:
            mod_2[grid[i][j]]+=1

ans=float("inf")
for i in range(C):
    for j in range(C):
        if i==j:
            continue
        for k in range(C):
            if k in [i,j]:
                continue

            total=0
            for prev,cnt in mod_0.items():
                total+=D[prev-1][i]*cnt
            for prev,cnt in mod_1.items():
                total+=D[prev-1][j]*cnt
            for prev,cnt in mod_2.items():
                total+=D[prev-1][k]*cnt
            
            ans=min(ans,total)
print(ans)