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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
typedef long long int ll;
typedef long double ld;
using namespace std;
const long long int INF = 1e18;
const long long int mod = 1e9+7;

typedef pair<ll, ll> pairs;
typedef vector<pairs> p;

struct Edge{
    ll to, weight;
    Edge(ll t, ll w) : to(t), weight(w){}
};
using graph = vector<vector<ll>>;
using Graph = vector<vector<Edge>>;


ll gcd(ll a,ll b){
    if(b == 0){
        return a;
    }else{
        return gcd(b, a%b);
    }
}

ll lcm(ll a, ll b){
    return a / gcd(a, b) * b;
}

ll keta(ll N){
    int tmp{};
    while( N > 0 ){
        tmp += ( N % 10 );
        N /= 10;
    }
    N = tmp;
    return N;
}

// 回文
bool kai(string S){
    bool flag = true;
    for(ll i=0;i<S.size()/2;++i){
        if(S[i] != S[S.size()-i-1]){
            flag = false;
            break;
        }
    }
    return flag;
}
// ---------------------------------------------

int main(){
    string s;
    cin>>s;

    ll ans = 0;
    ll n = s.size();
    bool flag = true;
    for(ll i=1;i<n;++i){
        if(s[i]-'0' != 9){
            flag = false;
            break;
        }
    }
    if(n == 1){
        ans += s[0]-'0';
    }else{
        ans += (n - 1) * 9;
        if(flag){
            ans += s[0]-'0';
        }else{
            ans += s[0]-'0' - 1;
        }
    }
    cout<<ans<<endl;

    return 0;
}