write a go solution for Description:
You are given a positive integer n.

Let S(x) be sum of digits in base 10 representation of x, for example, S(123)=1+2+3=6, S(0)=0.

Your task is to find two integers a,b, such that 0<=a,b<=n, a+b=n and S(a)+S(b) is the largest possible among all such pairs.

Input Format:
The only line of input contains an integer n (1<=n<=10^12).

Output Format:
Print largest S(a)+S(b) among all pairs of integers a,b, such that 0<=a,b<=n and a+b=n.

Note:
In the first example, you can choose, for example, a=17 and b=18, so that S(17)+S(18)=1+7+1+8=17. It can be shown that it is impossible to get a larger answer.

In the second test example, you can choose, for example, a=5000000001 and b=4999999999, with S(5000000001)+S(4999999999)=91. It can be shown that it is impossible to get a larger answer.. Output only the code with no comments, explanation, or additional text.