#include<fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int zero(int n)
{
	int r=0;
	while(n)
	{
		r+=n/5;
		n/=5;
	}
	return r;
}

int caut(int p)
{
	int st=1,dr=1<<30,mijl;
	while(st!=dr)
	{
		mijl=(st+dr)/2;
		if(zero(mijl)>=p)
			dr=mijl;
		else
			st=mijl+1;
	}
	if(zero(st)==p)
		return st;
	return -1;
}

int main()
{
	int p;
	in>>p;
	out<<caut(p);
	
	in.close();
	out.close();
	return 0;
}