#include <iostream>
using namespace std;
  
int main(){
    int i,n,c = 0;
    cin>>n;
    for(i = 1;i <= n;i++){
        if(i <= 99){
            if(i%10==0){
                c++;
            }
        }else{
            if(i/10%10==0||i%10==0){
                c++;
            }
        }
    }
    cout<<c;
}
/**************************************************************
	Problem: 1750
	User: wengsihan
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/