#include <bits/stdc++.h>
#define int long long
using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
int cate (int n)
{
	int pow = 5;
	int rez = 0;
	while (pow <= n)
		rez += n / pow, pow = pow * 5;
	return rez;
}
main()
{
	int n;
	in >> n;
	int st = 1, dr = 1LL<<62, poz = -1;
	while (st <= dr)
	{
		int mid = st + (dr - st) / 2;
		int zero = cate(mid);
		if (zero == n)
			poz = mid;
		if (zero < n)
			st = mid + 1;
		else
			dr = mid - 1;
	}
	out << poz << '\n';
}