#include<stdio.h>
long long int f(long long int n)
{
	long long int s = 1;
	while (s <= n)
		s *= 10;
	return s * s * n + s * n + n;
}
int main()
{
	long long int n;
	scanf("%lld", &n);
	long long int ans;
	for (ans = 1; f(ans) <= n; ans++);
	printf("%lld\n", ans - 1);
	return 0;
}