#include<fstream.h>
int main(){
ifstream in("fact.in");
ofstream out("fact.out");
long n,p,i,e=5,f=0,s=0,x=0,j=1;
in>>p;
i=1;
 if(p==0)
 out<<1<<"\n";
   else
   {while(s!=p)
    {
	i=1;
	if(j%e==0){
		f++;
		i=i+f;
		e=e*5;

	}
	s=s+i;
	x++;
	j++;
	if(s>p)
	out<<-1<<"\n";
    }

   out<<x*5<<"\n";}
   in.close();
   out.close();
   return 0;
}