#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
int check(int val)
{
  int s=0,x,f=5;
  x=val;
  while(x/f!=0)
  {
      s=s+x/f;
      f=f*5;
  }
  return s;
}
int cautbin()
{
    int l=1,r=500000000,sol,mid;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(check(mid)==p)
        {
            sol=mid;
            return sol;
        }
        else
            if(check(mid)<p)
            l=mid+1;
        else
            r=mid-1;
    }
}
int main()
{
fin>>p;
if(p==0)
    fout<<1;
else
    if(cautbin()==0)
    fout<<"-1";
else
    if(cautbin()>0)
    fout<<cautbin()-cautbin()%5;
}