#include<iostream>
#include<fstream.h>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

long long st,dr,p,mij,ct,i,aux,minim=2000000000;

int main()

{
	fin>>p;
	st=0;
	dr=2100000000;
			
	while(st<=dr)
	{   
		mij=(st+dr)/2;
		aux=mij;
		while(aux!=0)
		{
			ct+=aux/5;
			aux/=5;
		}
		
		if(p>ct)
			st=mij+1;
		
		if(p<ct)
			dr=mij-1;
	
		if(ct==p)
		{
			minim=mij;
			dr=mij-1;
		}
		ct=0;
	}
	
	if(p==5)
		fout<<"-1";
	else
		fout<<minim;
	return 0;
}