#include <fstream>
#include <cstdio>

int factorial(int p) {	
	int powerOfFive = 5, fiveMultipler = 0,
			fiveFactorCount = 0, logarithmBaseFive = 1;
	while (fiveFactorCount < p) {
		++fiveMultipler;
		if (fiveMultipler == powerOfFive) {
			powerOfFive *= 5;
			++logarithmBaseFive;
			fiveFactorCount += logarithmBaseFive;
		}
	  else
			++fiveFactorCount;
	}
	if (fiveFactorCount == p)
		return fiveMultipler * 5;
	return -1;
}

int main() {
	char const * const inputFile = "fact.in",
						 * const outputFile = "fact.out";
	std::ifstream in(inputFile);
	std::ofstream out(outputFile);

	int p = 0;
	while (in >> p)
		out << factorial(p) << std::endl;

	return 0;
}