#include<iostream>
using namespace std;
int main() {
	int N;
	cin >> N;
	int r = N / 3;
	int num = 1;
	while (true){
		if (r <= num * num) {
			break;
		}
		else {
			num *= 10;
		}
	}
	r = r / num;
	cout << r << endl;
}