#include <cstdio>

using namespace std;

int p, s, ci, i;
bool OK;

int main ()
{
	freopen ("fact.in", "r", stdin);
	freopen ("fact.out", "w", stdout);
	
	scanf ("%d", &p);
	
	for (i = 1;;i++)
	{
		s = 0;
		
		for (ci = i; ci > 0;)
		{
			ci /= 5;
			s += ci;
		}
		
		if (s == p) break;
		else if (s > p) {OK = true; break;}
	}
	
	if (!OK) printf ("%d\n", i);
	else printf ("-1\n");
	
	return 0;
}