#include<fstream>

using namespace std;

int n;



ifstream f("fact.in");

ofstream g("fact.out");



int check(int nr)

{

	int fives = nr / 5;

	int c = 5;
	int power = 1;

	while(c * 5 <= nr)

	{

		fives+=power;
		power++;
		c = c * 5;

	}

	return fives;

}



int search(long start,long end)

{

	long nr = (end + start) / 2;

	int fives = check(nr);

	if(fives == n) return nr;

	if(start == end) return -1;

	return (fives > n) ? search(start, nr-1) : search(nr+1, end);

}



int main()

{

	f>>n;

	long nr = search(1, 5*n);

	nr++;

	g<<nr;

	return 0;

}