我这串python被判RE

a=int(input())
s1=input()
s2=input()
c={'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9,'A':10,'B':11,'C':12,'D':13,'E':14,'F':15,
   'G':16,'H':17,'I':18,'J':19,'K':20,'L':21,'M':22,'N':23,'O':24,'P':25,'Q':26,'R':27,'S':28,
   'T':29,'U':30,'V':31,'W':32,'X':33,'Y':34,'Z':35}
c2=dict(zip(c.values(),c.keys()))
b1=0
b2=0
#下面两个for循环RE了
for everychar in s1:
    b1=b1*a+c[everychar]
for everychar in s2:
    b2=b2*a+c[everychar]
b1=b1+b2
v=[]
while b1!=0:
    v.insert(0,c2[b1%a])
    b1=b1//a
for everynum in v:
    print(everynum,end='')