#include<fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int p,rez = -1;
int check(int n)
{
	int aux1 = 0;
	for(int i = 5; i <= n; i*=5)aux1=aux1 + (n/i);
	return aux1;
}
int main()
{
	cin >> p;
	int st = 1,mid,dr = 1000000000,aux1;
	while(st <= dr)
	{
		mid = (dr - st)/2 + st;
		aux1 = check(mid);
		if (aux1 == p) rez = mid, dr = mid-1;
		else if (aux1 > p) dr = mid - 1;
				else st = mid + 1;
	}
	//if (rez == 100000010) cout << "-1";
	cout << rez;
}