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 <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define all(x) (x).begin (),(x).end()
#define sqrt(x) sqrt(abs(x))
#define re return
#define sz(x) ((int)(x).size ())
#define prev PREV
#define next NEXT

using ll = long long;
using ii = pair<int, int>;
using ld = long double;
using D = double;
using vi = vector<int>;
using vii = vector<ii>;
using vvi = vector<vi>;
using vs = vector<string>;

template<typename T> T abs (T x) { re x < 0 ? -x : x; }
template<typename T> T sgn (T x) { re x < 0 ? -1 : (x > 0 ? 1 : 0); }
template<typename T> T sqr (T x) { re x * x; }
template<typename T> T gcd (T a, T b) { re a ? gcd (b % a, a) : b; }

int n;
int m;
string s;

int main () {
	cin >> s;
	n = sz (s);
	int ans = 0, cur = 0;
	for (int i = 0; i < n; i++) {
		if (s[i] > '0') ans = max (ans, cur + s[i] - '1' + (n - i - 1) * 9);
		cur += s[i] - '0';
	}	
	ans = max (ans, cur);
	cout << ans << endl;
	return 0;
}