#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;
	int p5 = 0;
	int i = 1;
	while (p5 < p)
	{
		i++;
		p5 += numara(i, 5);
	}
	g << i;
	f.close();
	g.close();
	return 0;
}