#include<fstream>
using namespace std;
unsigned long n,p,st=1,dr,bla,t,nr,v[12],i,sol=0;
int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	dr=1000000000;
	while(st<dr)
	{
		nr=0;
		t=(st+dr)/2;
		bla=t;
		while(bla!=0)
		{
			nr=nr+bla/5;
			bla=bla/5;
		}
		if(nr==p)
			sol=t;
		if(nr>=p)
			dr=t;
		else
			st=t+1;
	}
	if(!sol)
		g<<"-1";
	else
		g<<sol;
}