#include<fstream.h>
#include<math.h>
__int64 p,f=1;
long n;
void main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	do
	{
		n++;
		f=f*n;
	}
	while(log10(f)<=p);
	if(log10(f)==p)
		g<<n;
	else
		g<<"-1";
}