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


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

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