#include <bits/stdc++.h>
using namespace std;

long long n, m = 0;

int main()
{
	cin >> n;

	for (long long i = 1; i < 100000; i++) {
		long long j = 10, u;

		while (j <= i)
			j *= 10;

		u = i * (1 + j + j * j);

		if (u <= n)
			m++;
		else
			break;
	}

	cout << m << endl;
}