#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i,j,h=0,a;
	cin>>n;
	for(i=1;i<=n;i++){
		j=i;
		while(j>0){
			a=j%10;
			j=j/10;
			if(a==0){
				h++; 
			} 
			break;
		}
	} 
	cout<<h;
}
/**************************************************************
	Problem: 1750
	User: linzihang
	Language: C++
	Result: Wrong Answer
****************************************************************/