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