#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 caut(long long st,long long dr,long long x)
	{
		long gasit=0;
		while(st<=dr&&!gasit)
		{
			m=(st+dr)/2;
			if(verifica(m)==x)
			
				gasit=1;
			
			else
				if(x>verifica(m))
						st=m+1;
						else
							dr=m-1; 
		}
		if(gasit==0)
			m=-1;
	}
int main()
{
		f>>p;
		caut(1,999999999,p);
		if(m!=-1)
		{
			while(m)
			{
				if(verifica(m)==p)
					m--;
				else
					break;
			}
			
				g<<m+1;
			
		}
			else
				g<<m;
		
		
			return 0;
	}