#include<iostream>
#include<fstream>

using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
unsigned long long i,n,c,b;
int main (){
	f>>n;
	c=1;b=n*100;
	for(i=2;n!=0 && i<b;i++){
		c*=i;
		if(c%10==0)
			c/=10,n--;
		
	}
	if(i==b)
		g<<-1;
	else
	g<<i-1;
}