#include<fstream>
using namespace std;

inline long int putere5 (long int n)
{
	long int i=0;

	while (n%5==0)
	{
		n /= 5;
		i++;
	}

	return i;
}

int main()
{
	long int p,n=0,k=0;

	fstream f ("fact.in", ios::in);
	fstream g ("fact.out", ios::out);

	f>>p;

	if (p == 0)
		g<<1;
	else
	{
		while (p > k)
		{
			n += 5;
			
			k += putere5(n);
		}

		g<<n;
	}

	return 0;
}