#include<iostream.h>
#include<fstream.h>
#include<math.h>
int main(void)
{
	long int p,i,j,k,m,l;
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	k=0;
	i=2;
	j=25;
	k=p*5;
	while(j<=k)
	{
		j=pow(5,i);
		l=j;
		m=1;
		while((j<=l*5-1)&&(j<=k))
		{
			j=j*m;
			k=k-5;
			m=m+1;
		}
		i=i+1;
	}
	if(p>4)
	g<<k+5;
	if((p<=4)&&(p!=0))
		g<<k;
	if(p==0)
		g<<1;
}