#include<fstream.h>

long h(long f);

int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");

	long p;

	fin>>p;

	fin.close();

	fout<<h(p);
	fout.close();
	return 0;
}

long h(long f)
{
	if (f==0)
	return 1;
	int R=0,i=0,g,x=0,y=0;

	while (R<f)
	{
		i++;
		g=i;

		while (g%2==0)
		{
			g=g/2;
			x++;
		}
		while (g%5==0)
		{
			g=g/5;
			y++;
		}
		if (y!=0 && x!=0)
		{
			if (y>x)
			R=x;
			else
			R=y;
		}

	}
	return i;
}