#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<iomanip>
#include<numeric>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
using namespace std;
typedef long long ll;
const int mod=1e9+7;
int main(){
	ll n;
	cin>>n;
	for(int i=1;;i++){
		string s=to_string(i);
		s+=s+s;
		if(stoll(s)>n)
			cout<<i-1<<endl,exit(0);
	}
}