#include <stdio.h>
int st,dr,c;
int n,p;
int main ()
{
    freopen ("fact.in","r",stdin);
	freopen ("fact.out","w",stdout);
	int i,aux;
	scanf ("%d",&p);
	if (p==0)
	{
		  printf ("1");return 0;
	}
	st=4*p-1;
	dr=5*p+1;
	while (st<dr)
	{
		  i=0;
	      c=(st+dr)/2;
	      aux=c;
	      while (aux)
	      {
                i+=aux/5;
                aux/=5;
          }
          if (i==p)
          {
				   printf ("%d",c);return 0;
          }
          if (i>p)
             dr=c;
          else if (i<p)
               st=c;
    }
	if (i==p)
       printf ("%d",c);
    else
        printf ("-1");
    return 0;
}