#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
long a,b,c,d,s,p,d1;

    fin>>p;
    if(p==0)
    fout<<1;
    else
    {a=1;b=200000000000000;
    int ok=0;
    while((a<=b)&&(!ok))
 {

    c=(a+b)/2;
    s=0;d=c;
         while(d)
         {
             s+=d/5;
             d=d/5;
         }
     if(s==p) ok=1;
     else
     if(s>p) b=c-1;
     else a=c+1;
     }
     if(ok)
     {
      d1=c-1;
      do{d=d1;
        s=0;
         while(d)
         {
             s+=d/5;
             d=d/5;
         }
         d1--;
      }
        while(s==p) ;
       fout<<d1+2;

     }
     else fout<<-1;



    }
    return 0;
}