#include<fstream>

using namespace std;

int n;



ifstream f("fact.in");

ofstream g("fact.out");



int check(int nr)

{

	int fives = 0;

	int c = 5;
	//g<<nr<<" has fives: "<<fives;	
	while(c <= nr)

	{

		fives+=nr/c;
		c = c * 5;

	}
	//g<<nr<<" has fives: "<<fives<<"\n";   

	return fives;

}



int search(long start,long end)

{

	int nr = (end + start) / 2;
	if(start>end)return -1;

	int fives = check(nr);
	if(fives==n & nr%5 ==0) return nr;

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

}



int main()

{

	f>>n;

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

	g<<nr;

	return 0;

}