Buggy python submission (verdict: Runtime Error):
4 3
0 12 71
81 0 53
14 92 0
1 1 2 1
2 1 1 2
2 2 1 3
1 1 2 2
428
k-mbp:ABC99 kaibe$ cat D.py 
N,C = map(int,input().split())

D = []
c = []

for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 

c1 = []
c2 = []
c3 = []

from itertools import product

for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])
val=[]
cnt=[[],[],[]]


for j in range(C):
    cnt[0].append(c1.count(j+1))
    cnt[1].append(c2.count(j+1))
    cnt[2].append(c3.count(j+1))

for i in product(range(C),repeat=3):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j in range(C):
            dif += D[j][i[0]] * cnt[0][j]
            dif += D[j][i[1]] * cnt[1][j]
            dif += D[j][i[2]] * cnt[2][j]
        val.append(dif)

print(min(val))

Fixed submission:
N,C = map(int,input().split())
 
D = []
c = []
 
for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 
 
c1 = []
c2 = []
c3 = []
 
from itertools import product
 
for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])
val=[]
cnt=[[],[],[]]
 
 
for j in range(C):
    cnt[0].append(c1.count(j+1))
    cnt[1].append(c2.count(j+1))
    cnt[2].append(c3.count(j+1))
 
for i in product(range(C),repeat=3):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j in range(C):
            dif += D[j][i[0]] * cnt[0][j]
            dif += D[j][i[1]] * cnt[1][j]
            dif += D[j][i[2]] * cnt[2][j]
        val.append(dif)
 
print(min(val))

Buggy python submission (verdict: Time Limit Exceeded):
N,C = map(int,input().split())

D = []
c = []

for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 

c1 = []
c2 = []
c3 = []

from itertools import product

for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])
val=[]

for i in product(range(C),repeat=3):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j in range(C):
            dif += D[j][i[0]] * c1.count(j+1)
            dif += D[j][i[1]] * c2.count(j+1)
            dif += D[j][i[2]] * c3.count(j+1)
        val.append(dif)

print(min(val))

Fixed submission:
N,C = map(int,input().split())
 
D = []
c = []
 
for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 
 
c1 = []
c2 = []
c3 = []
 
from itertools import product
 
for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])
val=[]
cnt=[[],[],[]]
 
 
for j in range(C):
    cnt[0].append(c1.count(j+1))
    cnt[1].append(c2.count(j+1))
    cnt[2].append(c3.count(j+1))
 
for i in product(range(C),repeat=3):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j in range(C):
            dif += D[j][i[0]] * cnt[0][j]
            dif += D[j][i[1]] * cnt[1][j]
            dif += D[j][i[2]] * cnt[2][j]
        val.append(dif)
 
print(min(val))

Buggy python submission (verdict: Runtime Error):
N,C = map(int,input().split())

D = []
c = []

for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 

c1 = []
c2 = []
c3 = []

from itertools import product

for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])

val=[]

for i in product(set(c1),set(c2),set(c3)):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j,k in product(range(N),repeat=2):
            dif += D[c[j][k]-1][i[(j+k)%3]-1]
        val.append(dif)

print(min(val))

Fixed submission:
N,C = map(int,input().split())
 
D = []
c = []
 
for i in range(C):
    D.append(list(map(int,input().split())))
for i in range(N):
    c.append(list(map(int,input().split()))) 
 
c1 = []
c2 = []
c3 = []
 
from itertools import product
 
for i,j in product(range(N),repeat=2):
    if (i+j)%3 == 0:
        c1.append(c[i][j])
    elif (i+j)%3 == 1:
        c2.append(c[i][j])
    else:
        c3.append(c[i][j])
val=[]
cnt=[[],[],[]]
 
 
for j in range(C):
    cnt[0].append(c1.count(j+1))
    cnt[1].append(c2.count(j+1))
    cnt[2].append(c3.count(j+1))
 
for i in product(range(C),repeat=3):
    dif = 0
    if i[0]!=i[1] and i[1]!=i[2] and i[2]!=i[0]:
        for j in range(C):
            dif += D[j][i[0]] * cnt[0][j]
            dif += D[j][i[1]] * cnt[1][j]
            dif += D[j][i[2]] * cnt[2][j]
        val.append(dif)
 
print(min(val))