#include<fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");
int  sol,p;
int check(int n) {
	int i;
	int s=0;
	for(i=5;i<=n;i=i*5){
		s+=n/i;
	}
	return s;
}
void cb(int st,int dr) {
	if(st<=dr){
		int mid=(dr+st)/2;
		if(check(mid)==p && mid%5==0){
			sol=mid;
			return ;
		}
		else {
			if(check(mid)>=p)
				cb(st,mid-1);
			else
				cb(mid+1,dr);
		}
	}
	
}
int main () {
	
	f>>p;
	sol=-1;
	cb(0,1<<29);
	if(sol==-1){
		g<<-1;
	}
	else
		g<<sol<<"\n";
	return 0;
}