1/4对998244353取模后为748683265

(1/a)%p=a**(p-2)%p

def ad(a, b, c):
    d = 1
    while(b):
        if b%2 == 1:
            d = (d*a)%c  #(a*b)%c=((a%c)*(b%c))%c
        a = (a*a)%c
        b = b//2
    return d

p = 998244353
print(ad(4, p-2, p))

#等价于
#print(4**(p-2)%p)

748683265