#include <fstream>

std::ifstream f("fact.in");
std::ofstream g("fact.out");

int main()
{
	int n, p, numarZerouri;
	int factorial;
	numarZerouri = 0;
	n = 1;
	factorial = 1;
	f >> p;
	while (numarZerouri < p)
	{
		n++;
		factorial *= n;
		while (factorial % 10 == 0)
		{
			numarZerouri++;
			factorial /= 10;
		}
		factorial = factorial % 10;
	}
	if (numarZerouri == p)
		g << n;
	else
		g << -1;
}