#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;
}
unsigned long long BS(unsigned long long n)
{
	while(li<ls)
	{
		lm = (li+ls)/2;
		v=nrz(lm);
		if(v==n)
			return lm;
		else
			if(v>n)
				ls=lm-1;
			else
				li=lm+1;
	}
	return -1;
}
int main ()
{
	unsigned long long nz;
	in>>nz;
	out<<BS(nz)<<'\n';
}