#include<fstream>
using namespace std;

int f5(int a)
{
	int x=a, f=0;
	while(x!=0)
	{
		if (x%5==0)
			{
				f++;
				x=x/5;
			}
		else 
			break;
	}
	return f;
}

int main()
{
	ifstream in("factorial.in");
	ofstream out("factorial.out");
	int p,n=0,c=0;
	in>>p;
	while(c<=p)
	{
		c=c+f5(n);
		n=n+5;
	}
	if(p<0)
		out<<-1;
	else if(p==0)
		out<<1;
	else
	out<<n;
	return 0;
}