#include<fstream>
#include<math.h>

int numara(int a, int b)
{
	int nr = 0;
	while (a%b == 0){
		a = a / b;
		nr++;
	}
	return nr;
}

int main()
{
	std::ifstream f("fact.in");
	std::ofstream g("fact.out");
	int p;
	f >> p;
	if (p < 1) g << 1;
	else
	{
		int p5 = 0;
		int i = 5;
		while (p5 < p)
		{
			i++;
			p5 += numara(i, 5);
		}
		g << i;
	}
	f.close();
	g.close();
	return 0;
}