#include<fstream.h>
#include<math.h>
ifstream f("fact.in");
ofstream g("fact.out");
long double p,n;
int main()
{f>>p;
 p=p*5;
 double i=1;
 while(pow(5,i)<=p) i++;
 i--;
 long double c;
 while(i>1)
	{c=floor(p/pow(5,i));
	 if(pow(5,i)*c==p)
		if(c>1) p=p-(c-1)*5;
		else {p=-1;break;}
	 else p=p-c*5;
	 i--;}
 if(p!=0) g<<p;
 else g<<1;
 f.close();
 g.close();
 return 0;
}