#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;
ifstream f("fact.in"); ///kruskal
ofstream g("fact.out");
int p, c, k;

int dc(int p) {
	int s = 1; 
	int d = 1000000000;
	int m, pos = -1, k5, c;
	while (s <= d) {
		m = s + (d - s) / 2;
		c = 5, k5 = 0;
		while (c <= m) k5 += m / c, c *= 5;
		if (k5 == p) {
			pos = m, d = m - 1;
		}
		else if (k5 > p) d = m - 1;
		else
			s = m + 1;
	}
	return pos;

}

int main()
{
	f >> p;
	g << dc(p);
	return 0;
}