#include<fstream>
using namespace std;
long long p,m;
int i;
ifstream f("fact.in");
ofstream g("fact.out");
int verifica(long long k)
{
	int nr=0;
	while(k)
	{
		nr=nr+k/5;
		k=k/5;
	}
	return nr;
}
void cautarebinara(long long st,long long dr,long long x)
{
	long long gasit=0;
	while(st<=dr&&gasit==0)
	{
		m=(st+dr)/2;
		if(verifica(m)==x)
		{
		   // g<<m;
			gasit=1;
		}
		else
			if(x>verifica(m))
					st=m+1;
			else
				dr=m-1;
			//else
				
	}
	if(gasit==0)
	{
		m=-1;
		//g<<-1;
	}
}
int main()
{
	f>>p;
	cautarebinara(1, 999999999,p);
	if(m!=-1)
	{
    	while(m)
	     {
		if(verifica(m)==p)
			m--;
		else
			break;
	    }
	g<<m+1;
	}
	else
		g<<m;

	return 0;
}