#include <fstream>
using namespace std;

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

int nr(int n)
{
	int S,y;
	for(S = 0,y = 5; y <= n; S += n/y,y *=5);
	return S;
}

int main()
{
	int p,li,ls,mid;
	fin>>p;
	li = 4 * p; ls = 5 * p;
	while(li <= ls)
	{
		mid = (li + ls)>>1;
		if(nr(mid) >= p)
			ls = mid - 1;
		else
			li = mid + 1;
	}
	if(nr(li) != p)
		fout<<-1<<'\n';
	else
	fout<<li<<'\n';
	return 0;
	
}