Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 14:11:52 2019

@author: adachi-lab
"""

input_code = str(input())
L1 = len(input_code)

list_3 = []
for w in range(L1):
    list_3.append(w)


x = 0
for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3.remove(x)
    
    x+=1

L3 = len(list_3)
list_4 = []

if list_3[0] == 0:
    for q in range(L3-1):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3-1]-1)
    
    
else:
    list_3.insert(0,0)
    list_4.append(list_3[1])
    for q in range(L3):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3]-1)
    list_4.pop(1)
    
    


print(max(list_4))

Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 16:48:09 2019

@author: adachi-lab
"""

input_code = input()
L1 = len(input_code)
list_3 = []
list_4 = []
list_5 = []

for w in range(L1):
    list_3.append(0)
    list_4.append(0)


for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3[i] = 1
        
c = 0

for n,m in zip(list_3,list_4):
    
    if n == m:
        c = 0
        list_5.append(c)
        
    else:
        c += 1
        list_5.append(c)
        
print(max(list_5))

Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 14:11:52 2019

@author: adachi-lab
"""

input_code = str(input())
L1 = len(input_code)

list_3 = []
for w in range(L1):
    list_3.append(w)


x = 0
for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3.remove(x)
    
    x+=1

L3 = len(list_3)
list_4 = []

if list_3[0] == 0:
    for q in range(L3-1):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3-1]-1)
    
    
else:
    list_3.insert(0,0)
    list_4.append(list_3[1])
    for q in range(L3):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3]-1)
    list_4.pop(1)
    
    


print(max(list_4))

Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 16:48:09 2019

@author: adachi-lab
"""

input_code = input()
L1 = len(input_code)
list_3 = []
list_4 = []
list_5 = []

for w in range(L1):
    list_3.append(0)
    list_4.append(0)


for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3[i] = 1
        
c = 0

for n,m in zip(list_3,list_4):
    
    if n == m:
        c = 0
        list_5.append(c)
        
    else:
        c += 1
        list_5.append(c)
        
print(max(list_5))

Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 14:11:52 2019

@author: adachi-lab
"""

input_code = str(input('入力;'))
L1 = len(input_code)

list_3 = []
for w in range(L1):
    list_3.append(w)


x = 0
for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3.remove(x)
    
    x+=1

L3 = len(list_3)
list_4 = []

if list_3[0] == 0:
    for q in range(L3-1):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3-1]-1)
    print(list_4)
    
else:
    list_3.insert(0,0)
    list_4.append(list_3[1])
    for q in range(L3):
        list_4.append(list_3[q+1]-list_3[q]-1)
    list_4.append(L1-list_3[L3]-1)
    list_4.pop(1)
    print(list_4)
    


print(max(list_4))

Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Fri Apr  5 16:48:09 2019

@author: adachi-lab
"""

input_code = input()
L1 = len(input_code)
list_3 = []
list_4 = []
list_5 = []

for w in range(L1):
    list_3.append(0)
    list_4.append(0)


for i in range(L1):
    code = input_code[i]
    if code == 'A' or code == 'C' or code == 'G' or code == 'T':
        list_3[i] = 1
        
c = 0

for n,m in zip(list_3,list_4):
    
    if n == m:
        c = 0
        list_5.append(c)
        
    else:
        c += 1
        list_5.append(c)
        
print(max(list_5))