#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i=1,h=0,a=0;
	cin>>n;
	while(i<=n){
		h=h+i%10;
		i=i/10;
		if(h=10){
			a+=1;	
		}
		i++;	
	} 
	cout<<a;
}
/**************************************************************
	Problem: 1985
	User: hongjiaming
	Language: C++
	Result: Time Limit Exceed
****************************************************************/