#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long n,p,li,ls,m,nr,z;
int main()
{f>>p;
if(p==0)
  g<<0<<'\n';
  else
{li=1;
ls=100000000;
while(li<=ls)
     {m=(ls+li)/2;
     nr=0;
     z=5;
     while(z<m)
	  {nr=nr+m/z;
	  z=z*5;
	  }
     if(nr==p)
       break;
       else
       if(nr>p)
	 ls=m-1;
	 else
	 li=m+1;
     }
if(li>ls)
  g<<-1<<'\n';
  else
  {while(m%5!=0)
       m--;
  g<<m<<'\n';
  }
}
f.close();
g.close();
return 0;
}