#include <fstream>

using namespace std;

ifstream fin ("fact.in");
ofstream fout ("fact.out");

int p, n, r, c, suma;

int main (){

      fin>>p;

      for (r = 1; ;r++) {
            /// calculez cati de 0 are la final r!
            c = 5;
            suma = 0;
            while (c <= r) {
                  suma += r/c;
                  c *= 5;
            }
            if (suma == p) {
                  fout<<r;
                  break;
            }
            if (suma > p) {
                  fout<<-1;
                  break;
            }
      }

      return 0;
}