Buggy python submission (verdict: Runtime Error):
K  = int(input())
n = 0
n1 = 0
n2 = 0
n3 = 0
n4 = 0
n5 = 0


#Kが500以下の場合、斜め作戦にする
if K <= 500:
   n = K
   mat = [[0 for n1 in range(K)] for n2 in range(K)]
   for n1 in range(K):
      for n2 in range(K-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(K):
      for n2 in range(n1):
         mat[n1][n2] = K+n2-n1+1

#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   n = 500
   mat = [[0 for n1 in range(500)] for n2 in range(500)]
   for n1 in range(500):
      for n2 in range(500-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(500):
      for n2 in range(n1):
         mat[n1][n2] = 500+n2-n1+1










#行列の出力かんがえとく 
print(n)

if K <= 500:
out = ""
for n1 in range(K):
   out = ""   
   for n2 in range(K):
      out = out + " " + str(mat[n1][n2])
   print(out)
#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
out = ""
for n1 in range(500):
   out = ""   
   for n2 in range(500):
      out = out + " " + str(mat[n1][n2])
   print(out)





Fixed submission:
K  = int(input())
n = 0
n1 = 0
n2 = 0
n3 = 0
n4 = 0
n5 = 0


#Kが500以下の場合、斜め作戦にする
if K <= 499:
   n = K
   mat = [[0 for n1 in range(K)] for n2 in range(K)]
   for n1 in range(K):
      for n2 in range(K-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(K):
      for n2 in range(n1):
         mat[n1][n2] = K+n2-n1+1

#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   n = 500
   mat = [[0 for n1 in range(500)] for n2 in range(500)]
   for n1 in range(500):
      for n2 in range(500-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(500):
      for n2 in range(n1):
         mat[n1][n2] = 500+n2-n1+1

   #Kが500以上の場合のギザギザ部分
   for n2 in range(K-500):
      for n1 in range(250):
          kari = n1*2+n2
          if kari >= 500:
             kari = kari-500
          mat[n1*2][kari] = n2+501


#行列の出力かんがえとく 
print(n)

if K <= 500:
   out = ""
   for n1 in range(K):
      out = ""   
      for n2 in range(K):
         out = out + " " + str(mat[n1][n2])
      print(out)
   
#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   out = ""
   for n1 in range(500):
       out = ""   
       for n2 in range(500):
          out = out + " " + str(mat[n1][n2])
       print(out)

Buggy python submission (verdict: Runtime Error):
K  = int(input())
n = 0
n1 = 0
n2 = 0
n3 = 0
n4 = 0
n5 = 0


#Kが500以下の場合、斜め作戦にする
if K <= 500:
   n = K
   mat = [[0 for n1 in range(K)] for n2 in range(K)]
   for n1 in range(K):
      for n2 in range(K-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(K):
      for n2 in range(n1):
         mat[n1][n2] = K+n2-n1+1

#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   n = 500
   mat = [[0 for n1 in range(500)] for n2 in range(500)]
   for n1 in range(500):
      for n2 in range(500-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(500):
      for n2 in range(n1):
         mat[n1][n2] = 500+n2-n1+1










#行列の出力かんがえとく 
print(n)
out = ""
for n1 in range(K):
   out = ""   
   for n2 in range(K):
      out = out + " " + str(mat[n1][n2])
   print(out)





Fixed submission:
K  = int(input())
n = 0
n1 = 0
n2 = 0
n3 = 0
n4 = 0
n5 = 0


#Kが500以下の場合、斜め作戦にする
if K <= 499:
   n = K
   mat = [[0 for n1 in range(K)] for n2 in range(K)]
   for n1 in range(K):
      for n2 in range(K-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(K):
      for n2 in range(n1):
         mat[n1][n2] = K+n2-n1+1

#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   n = 500
   mat = [[0 for n1 in range(500)] for n2 in range(500)]
   for n1 in range(500):
      for n2 in range(500-n1):
         mat[n1][n1+n2] = n2+1
   for n1 in range(500):
      for n2 in range(n1):
         mat[n1][n2] = 500+n2-n1+1

   #Kが500以上の場合のギザギザ部分
   for n2 in range(K-500):
      for n1 in range(250):
          kari = n1*2+n2
          if kari >= 500:
             kari = kari-500
          mat[n1*2][kari] = n2+501


#行列の出力かんがえとく 
print(n)

if K <= 500:
   out = ""
   for n1 in range(K):
      out = ""   
      for n2 in range(K):
         out = out + " " + str(mat[n1][n2])
      print(out)
   
#Kが500以上の場合、斜めに1マスずつしのびこませる   
else:
   out = ""
   for n1 in range(500):
       out = ""   
       for n2 in range(500):
          out = out + " " + str(mat[n1][n2])
       print(out)