#include<fstream>
using namespace std;
int p,nr,n,m;
int cautare_binara(int st,int dr)
{
	int k,sol=-1;
	while(st<=dr)
	{
		m=st+(dr-st)/2;
		nr=0;
		k=5;
		n=m;
		while(n/k)
		{
			nr+=n/k;
			k*=5;
		}
		if(nr==p)
			sol=m;
		if(nr<p)
			st=m+1;
		else dr=m-1;
	}
	return sol;
}
		
int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	fin>>p;
	if(p==0)
		fout<<'1\n';
	else
	fout<<cautare_binara(1,5*p)<<'\n';
	
	return 0;
}