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

int main()
{
	string N;
	cin >> N;

	int sz = N.size();
	int ans = 0;
	int st = 1;
	for( int i = 3; i <= sz; i += 3 ) {
		int ed = st * 10;
		if( i < sz ) ans += ed - st;
		else {
			long long n = atoll( N.c_str() );
			int m = sz / 3;
			long long l = 1;
			for( int j = 0; j < m; j++ ) l *= 10;
			for( long long j = st; j < ed; j++ ) {
				long long a = j;
				a += j * l;
				a += j * l * l;
				if( a > n ) break;
				ans++;
			}
		}
		st *= 10;
	}

	cout << ans << endl;
}