#include <fstream>
#include <cmath>
using namespace std;

int main()
{
	int n, primul=0, descazut=0, i;
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>n;
	if(n==0)
		g<<1;
	else
	{
	primul=n*5;
	for(i=2; i<=11; i++)
	{
		int lol=round(pow((double)5, (double)i));
		for(int j=lol; j<=primul; j+=lol)
		{
			primul-=5;
		}
	}
	g<<primul;
	}
}