#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int n,st,dr,m;
int f(int a)
{
	int x=0,c=5;
	while(a>=c){
		x+=a/c;
		c*=5;
	}
	return x;
}
int main()
{
	in>>n;
	st=1;dr=5*n;
	while(st<=dr){
		m=((st+dr)>>1);
		if(f(m)<n)
			st=m+1;
		else
			dr=m-1;
	}
	if(f(st)==n)
		out<<st;
	else 
		out<<"-1";
	return 0;
}