#include <fstream>
using namespace std;

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

int factorial (int n)
{
	int r=0,i;
	for (i=5;i<=n;i*=5)
		r+=n/i;
	return r;
}

int bsearch (int x)
{
	int i,step=1<<30;
	for (i=0;step;step>>=1)
		if (factorial(i+step)<x)
			i+=step;
	if (factorial(i+1)==x)
		return i+1;
	return -1;
}

int main()
{
	int p;
	in>>p;
	out<<bsearch(p)<<"\n";
	return 0;
}