#include <iostream>
using namespace std;
#include <fstream>

namespace pb_006_factorial_nms
{
	int f(int p, int N)
	{
		int t = N;
		int power = 0;
		while ( (t = t/p) ) power += t;	

		return power;
	}

	int binary_search_for_N(int P)
	{
		if (P == 0) return 1;
		//otherwise
		int MAX_N = 500000000;	
		int a = 1, b = MAX_N;

		int f_a = f(5, a), f_b = f(5, b), f_bm1 = f(5, b-1), f_m;
		//binary search
		while ( !(f_bm1 < P && P <= f_b) ) //f(b-1) < P <= f(b) is the end condition
		{
			int m = a + (b-a)/2;
			f_m = f(5, m);
			if (f_m < P) { a = m; f_a = f_m; }
			else /* P <= f_m */ { b = m; f_b = f_m; f_bm1 = f(5, b-1); }		
		}

		if (f_b == P) return b;
		else return -1;
	}
}
//int pb_006_factorial()
int main()
{
	using namespace pb_006_factorial_nms;
	char* in_file = "fact.in";
	char* out_file = "fact.out";

	int P;

	ifstream ifs(in_file);
	ifs>>P;
	ifs.close();

	ofstream ofs(out_file);	
	ofs<<binary_search_for_N(P);
	ofs.close();

	return 0;
}