#include<stdio.h>

//using namespace std;

int factorial(int zero, int &x,int n) {
	//long x=j;
	//for (long i=n-1 ; i<=n ; i++) {
		x=x*n;
		while (x%10==0 && x/10!=0) {
			zero++;
			x=x/10;
		}
		x=x%10;
	//}
	return zero;
}

int main() {
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	int p,n=1,zero=0,x=1;
	scanf("%d\n", &p);
	while (zero<p) {
		n++;
		zero=factorial(zero,x,n);
	}
	if (zero>p) printf("-1\n");
	else printf("%d\n",n);
	return 0;
}