#include<iostream>
using namespace std;
#include<fstream>

int main()
{
	int P,x,nr_curent=1;
	ifstream f_in("fact.in");
	ofstream f_out("fact.out");
	f_in>>P;
	if(P==0)
	{
		f_out<<nr_curent;
	}
	else
	{
		while(P>0)
		{
			x=nr_curent;
			while(x%5==0)
			{
				P--;
				x=x/5;
			}
			while(x%10==0)
			{
				P--;
				x=x/10;
			}
			nr_curent++;
		}
		f_out<<nr_curent-1;
	}
	if(P!=0)
		f_out<<-1;
	return 0;
}