#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
int v[16];
main()
{
	int p,i,x,j,s=0;
	f>>p;
	x=p;
	for(i=0;i<=12;i++)
	{
		v[i]=p/(pow(5,i));
		s+=(i+1)*v[i];
	}
	while(s>p)
	{
		i=0;
		if (s>p+100000)
		v[i]-=500;
		else 
		v[i]--;
		s=0;
		s+=v[i];
		for(j=i+1;j<=12;j++)
			{
				v[j]=v[j-1]/5;
				s+=v[j];
			}
	}
	if (p)	
		g<<v[0]*5;
else g<<"0";
}