Problem:
Score : 300 points

Problem Statement

Find the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Constraints

1\leq N \leq 10^{16}

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Sample Input 1

100

Sample Output 1

18

For example, the sum of the digits in 99 is 18, which turns out to be the maximum value.

Sample Input 2

9995

Sample Output 2

35

For example, the sum of the digits in 9989 is 35, which turns out to be the maximum value.

Sample Input 3

3141592653589793

Sample Output 3

137

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<cstdio>
long long n;
int main() {
	scanf("%lld", &n);
	long long t = 1, nn = n, s = 0;
	while (nn/10) {
		nn /= 10;
		t *= 10;
		s += 9;
	}
	if ((nn + 1)*t - 1 <= n) {
		s += nn;
	}
	else s += (nn - 1);
	printf("%lld\n", s);
}