#include <fstream>
using namespace std;

ifstream f("fact.in");
ofstream f2("fact.out");

int main() {
	long k=0,p=0,n,i=0;
	f>>n;
	if(n==0) {
		p=n;
		k=1;
	} else {
		while(p<n) {
			k+=25;
			i+=5;
			p+=5;
			int aux=i;
			while(aux%5==0) {
				p++;
				aux/=5;
			}
		}
		while(p>n) {
			k--;
			i--;
			p--;
			int aux=i+1;
			while(aux%5==0) {
				p--;
				aux/=5;
			}
		}
	}
	if(p==n) f2<<k; else f2<<-1;
	return 0;
}