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

long zero(int 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;
	}
	mijl=(st+dr)/2;
	//if(v[mijl]>val) 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);
	//
	 //else 
		// if(k!=p) g<<-1;
			//else g<<n;
	
}