#include<bits/stdc++.h>
#define int long long
#define matsuri pair<int,int>
//const int iris = 1e9+7;
const int iris = 998244353;
using namespace std;

void solve()
{
	int n;
	cin>>n;
	int l=1, r=1e5;
	auto cal=[](int a)
	{
		int d=1;
		while(d<=a)
			d*=10;
		return a*d*d+a*d+a;
	};
	while(l<r)
	{
		int m=l+(r-l)/2;
		if(cal(m)>n)
			r=m;
		else
			l=m+1;
	}
	cout<<r-1<<'\n';
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);

	int T=1;
	//cin>>T;
	while(T--)
		solve();

	return 0;
}