#include <stdio.h>
FILE *fin,*fout;
long long d10,d5,i,nr,n,aux;

long long des (long long x,long long &y)
    {int j=0;
    while (y%x==0){ y=y/x;j++;}

    return j;
    }


int main()

{
fin=fopen("fact.in","rt");
fout=fopen("fact.out","wt");
fscanf(fin,"%lld",&n);

i=0;
while (1)
  {i+=5;
  if (nr==n)
     {
      fprintf (fout,"%lld\n",i-5);
      break;
     }
  if (nr>n)
     {
     fprintf (fout,"-1\n");
     break;
     }
  aux=i;
  d10=0;
  d5=0;
  d10=des(10,aux);
  d5=des(5,aux);
  nr=nr+d5+d10;
  }



fcloseall();
return 0;
}