#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i,j,b,h=0;
	cin>>n;
	for(i=1;i<=n;i++){
		j=i;
		while(j>0){
			b=j%10;
			j=j/10;
			if(b==0){
				h++;
			}
			continue;
		}
	}
	cout<<h;
}

/**************************************************************
	Problem: 1750
	User: linzihang
	Language: C++
	Result: Wrong Answer
****************************************************************/