#include<fstream>
using namespace std;
int p;
int zero(int x);
int main();
int factorial()
{
	int i;
	int pas=1<<30;
	for(i=0;pas!=0;pas/=2)
		if(zero(i+pas)<p)
			i+=pas;
	if(zero(i+pas+1)==p)
		return i+pas+1;
	else
		return -1;
}
int zero(int x)
{
	int ct=0;
	while(x>=5)
	{
		ct+=x/5;
		x=x/5;
	}
	return ct;
}
int main()
{
	fstream in,out;
	in.open("fact.in",ios::in);
	out.open("fact.out",ios::out);
	in>>p;
	out<<factorial();
	in.close();
	out.close();
}