#include<fstream>
using namespace std;
int main()
{
	ifstream in ("fact.in");
	ofstream out("fact.out");
	long int p,nrtz,i,ii,p2=1;
	in>>p;
	nrtz=5*p;
	for (i=5;i<=nrtz;i+=5)
	{ii=i/5;
	 while(ii%5==0)
	{ nrtz=nrtz-5;
      ii=ii/5;
	}
	}
	if((nrtz+5)%25==0)
		{ for(i=5;i<=nrtz;i=i+5)
			{ii=i;
			if (ii%5==0) while(ii!=0)
							{ if(ii%5==0) p2++;
							  ii=ii/5;
							}
		}   }
	
	if(p==p2) nrtz=-1;
	if (nrtz==0) nrtz =1;
	out<< nrtz;
	in.close();
	out.close();
	return 0;
}