#include<stdio.h>

FILE *in;
FILE *out;

int main()
{

in=fopen("factorial.in","r");
out=fopen("factorial.out","w");
int p,nr,n,aux,i;
n=1;nr=0;
fscanf(in,"%d",&p);
while(nr<p)
{
  aux=n;
  nr=0;
  i=5;
  while(aux/i)
   {
     nr+=aux/i;
     i*=5;
   }
  n++;

}
 if (nr==p) fprintf(out,"%d\n",n-1);
 else if(p==0) fprintf(out,"%d\n",'1');
 else fprintf(out,"%d\n",'-1');




return 0;
}