#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
unsigned long long li = 1;
unsigned long long ls = 1220703125 ;
unsigned long long v=0;
unsigned long long lm;
unsigned long long nrz(unsigned long long nr)
{
	unsigned long long n = 0;
	while(nr)
	{
		n+=nr/5;
		nr/=5;
	}
	return n;
}
int main ()
{
	unsigned long long n;
	in>>n;
	while(li<ls)
	{
		lm = (li+ls)/2;
		v=nrz(lm);
		if(v==n)
		{
			while(nrz(lm)==n)lm--;
			out<<lm+1<<'\n';
			return 0;
		}
		else
			if(v>n)
				ls=lm-1;
			else
				li=lm+1;
	}
	out<<'-1';
	return 0;
}