#include <fstream>

int nr_zerouri(int n) {
	int nr = 0;
	long long p = 1;
	for (int i = 5; i <= n; i *= 5)
		nr += n / i;

	return nr;
}

int main()
{
	std::ifstream fin("fact.in");
	std::ofstream fout("fact.out");

	int p, n = 1;
	fin >> p;

	int k = nr_zerouri(n);

	while (k < p) {
		n++;
		k = nr_zerouri(n);
	}

	if (k == p)
		fout << n;

	else
		fout << -1;

	fin.close(), fout.close();

	return 0;
}