#include <fstream>
using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
long long n,nr2,nr5,aux;
float ii;
int main()
{
    fin>>n;
    if(n==0)
        fout<<1<<'\n';
    else
        {
            int i=0;
            while(nr5<n)
                {
                  i++;
                  ii=i;
                  aux=i;
                  while(aux/5==ii/5&&aux!=1)
                  {
                      nr5++;
                      aux=aux/5;
                      ii=aux;
                  }

                }
         if(nr5==n)
            fout<<i<<'\n';
         else
            fout<<-1<<'\n';
        }
    return 0;

}