luogu ide上面没问题，但是评测会WA

n = int(input())
m = list(input())[::-1]
count = 0
def add(nm,n):
    lm = len(nm)
    num = [0]*lm
    for i in range(lm):
        num[i] += nm[i]+nm[lm-1-i]
        if num[i] >=n:
            num[i] %= n
            if i != lm-1:
                num[i+1] += 1
            else:
                num.append(1)
    return num
for i in range(len(m)):
    if m[i].isalpha():
        m[i] = ord(m[i])-55
    else:
        m[i] = ord(m[i])-48
while m[::-1] != m:
    m = add(m,n)
    count += 1
print("STEP="+str(count))