#include <fstream>
#include <cmath>

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

long long zeros(long long p)
{
	long long x = 0;
	for (long long i = 1; i <= p; i++)
	{
		x += p / pow(5, i);
	}
	return x;
}

int main(){
	
	long long int P, p, s;
	bool ok = true;

    fin >> P;
	
	p = 4 * P;

    do
	{
		s = zeros(p);
		if (s == P)
		{
			ok = 0;
		}
		else if (s > P)
		{
			p = -1;
			ok = 0;
		}
		else p++;
		
	} while (ok);

    fout << p;

    fin.close();
    fout.close();
	
	return 0;
}