#include <fstream>

using namespace std;
ifstream fin("factorial.in");
ofstream fout("factorial.out");
const long long NMAX = 1000000000;
long long legendre(long long n)
{
     long long numitor = 5;//nr prim
     long long p = 0; //putere

      while(numitor <=n)
      {
          p = p + n/numitor;
          numitor = numitor*5;
      }
      return p;
}
int main()
{

    long long st  = 1, dr = NMAX, solutie = -1, n, p, mid;
     fin>>p;
    while(st<=dr)
    {
        mid = (st + dr) >>1;
        n = legendre(mid);
        if(n == p)
        {
           solutie = mid;
           dr = mid - 1;
           continue;
        }
        if(n < p)
          st = mid + 1;
        else
          dr = mid - 1;
    }
    fout<<solutie<<"\n";
    return 0;
}