#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int n,P,X,nr,i;
int main()
{
   in=fopen("fact.in","r");
   out=fopen("fact.out","w");
   fscanf(in,"%d",&P);
   for(i=5;nr<P;i=i+5)
   {
       X=i;
       while(X%5==0)
             {
                 X=X/5;
                  nr++;
             }

   }

   if(P>0)
{
    if(nr==P)
fprintf(out,"%d",i-5);
   else
       if(  nr>P)
   fprintf(out,"%d",-1);


}
else
fprintf(out,"%d",nr);



   fclose(in);fclose(out);
    return 0;
}