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