#include<iostream>
#include<fstream>
using namespace std;
long long p;
long n,k;

long zero(long nr)
{
	int k=0;
	while(nr>=5)
	{
		k=k+nr/5;
		nr/=5;
	}
	return k;
}

long cautare (long st, long dr, long val)
{
	int mijl;
	while(st<dr)
	{
		mijl=(st+dr)/2;
		if(zero(mijl)>=val) dr=mijl-1;
			else st=mijl+1;
	}
	
	if(zero(mijl)==val) return mijl;
		else 
			mijl++;
		
	if(zero(mijl)==val) return mijl;
	return -1;
}
int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	n=0;
	k=0;
	if(p==0) g<<1;
		else g<<cautare(1,5*p,p);
	return 0;
}