#include<fstream.h>
int main(){
ifstream fin("fact.in");
ofstream fout("fact.out");
long int  P,nr,x=0,N=0;
fin>>P;
if (P==0)
   fout<<1;
   else
 /*  while (N!=P){
	 x+=5;
	 nr=x;
	while (nr%5==0){
	       nr/=5;
	       N++;}
	  }  */
    N=P*5;
    long int e=N;
    x=0;
    short y=0;
    while (x<e-25) {
	x+=25;
	nr=x;
	y=0;
	while (nr%5==0){
	       nr/=5;
	       y++;}
	    for (short i=1;i<y;i++)
		  N-=5; }
if (P<0)
fout<<-1;
else
fout<<N;
fin.close();
fout.close();
return 0;
}