#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long p,n,m,st,x,dr,mid;

int verif(int mid){
	int nr=0; int p=5;
	while(mid/p>0) nr+=mid/p, p*=5;
	return nr;
}

int main()
{
	f>>p;
	
	if(p==0){
		g<<0; return 0;
	}
	
	st=5;
    dr=400000015;
	
	while(st<=dr){
		mid=st+dr; mid/=2;
		x=verif(mid);
		if(x==p)
			break;
		else
			if(x<p)
				st=mid+1;
			else
				dr=mid-1;
	}
	if(st<=dr)
		g<<mid/5*5;
	else
		g<<-1;
	return 0;
}