#include<stdio.h>
int main()
{
	long long int n;
	scanf("%lld", &n);
	long long int min, mid, max;
	max = n;
	min = 0;
	while (max - min > 1)
	{
		mid = (max + min) / 2;
		if (3 * mid * mid <= n)
			min = mid;
		else
			max = mid;
	}
	printf("%lld\n", min);
	return 0;
}