#include<iostream>
#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main ()
{
	long long n,p,nr=0,zero=1,factorial;
	f>>p;
	n=1;
	if(nr==p)
		g<<n;
	for(int j=1;j<=p;j++)
		zero=zero*10;
	while (zero!=p)
	{
		n++;
		factorial=1;
		for(int i=1;i<=n;i++)
			factorial=factorial*i;
		if(factorial%zero==0)
		{
			g<<n;
			break;
		}
	}
}