#include <iostream>

using namespace std;

int main(int argc, const char* argv[])
{
	uint64_t N;
	cin >> N;
	uint64_t b = (uint64_t)1e9 + 1;
	//	1~9
	//	11~99
	//	111~999
	//	...
	//	11111111~99999999
	int cnt = 0;
	N /= b;
	while (N > 0) {
		cnt += N >= 10 ? 9 : N % 10;
		N /= 10;
	}
	cout << cnt << endl;
	return 0;
}