#include <stdio.h>
int main()
{
int p,k,i,z,supergenial;
unsigned long  n,emi;
FILE *fin, *fout;
fin=fopen("fact.in","r");
scanf("%d",&p);
n=1;
i=1;
z=0;
while (((supergenial<p)||(supergenial>p))&&(n<=1000000))
 {
 n*=i;//calculeaza factorialul
 i++;
 z=0;//indicator pt nr de 0-uri ale lui n
 emi=n;//salvez valoarea lui n pt a nu se pierde
 k=0;
 supergenial=0;
	while ((emi%5==0)&&(supergenial<=p))
	{emi=emi/5; 
	supergenial++;}
 
};
  fclose(fin);
  fout=fopen("fact.out","w");
  if (z==p) fprintf(fout,"%d",i);
  else fprintf(fout,"-1");
  fclose(fout);
  return 0;
}