Problem Statement

For integers $b (b \geq 2)$ and $n (n \geq 1)$, let the function f(b,n) be defined as follows:

• f(b,n) = n, when n < b
• f(b,n) = f(b,$,{\rm floor}(n / b)) + (n$${\rm mod}$\ b),$n \geq b$

Here, ${\rm floor}(n / b)$ denotes the largest integer not exceeding n / b,
and n \ ${\rm mod}$ \ b denotes the remainder of n divided by b.
Less formally, f(b,n) is equal to the sum of the digits of n written in base b.
For example, the following hold:

• f(10,\,87654)=8+7+6+5+4=30
• f(100,\,87654)=8+76+54=138

You are given integers n and s.
Determine if there exists an integer $b (b \geq 2)$ such that f(b,n)=s.
If the answer is positive, also find the smallest such b.

Input

The input is given from Standard Input in the following format:
n
s

Output

If there exists an integer $b (b \geq 2)$ such that f(b,n)=s, print the smallest such b.
If such b does not exist, print -1 instead.

Constraints

• $1 \leq n \leq 10^{11}$
• $1 \leq s \leq 10^{11}$
• n,\,s are integers.

Sample Input 1

87654
30

Sample Output 1

10

Sample Input 2

87654
138

Sample Output 2

100

Sample Input 3

87654
45678

Sample Output 3

-1

Sample Input 4

31415926535
1

Sample Output 4

31415926535

Sample Input 5

1
31415926535

Sample Output 5

-1

见题面 Input 部分

见题面 Output 部分