#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{ int p,n,put,fact,s;

    fin>>p;
    if(p==1)
    fout<<1;
    else
    {n=1;
     do
     {
         n++;
         s=0;
         put=5;
         while(n/put!=0)
         {
             s+=n/put;
             put*=5;
         }


     }while(s<p);
     if(s==p) fout<<n;
     else fout<<-1;



    }
    return 0;
}