#include <stdio.h>

FILE* f;

int main()
{

	int p;

	f=fopen ("fact.in","r");
	fscanf (f,"%d",&p);
	fclose (f);

	int n=0;
	int f5=0;
	int factor;
	while (f5<p)
	{
		f5=0;
		for (factor=5;factor<=n;factor=factor*5)
			f5=f5+(n/factor);

		n+=5;
	}

	f=fopen ("fact.out","w");
	if (f5==p)
	{
		if (p!=0)
			fprintf (f,"%d",n-5);
		else
			fprintf (f,"%d",1);
	}
	else
		fprintf (f,"%d",-1);
	fclose (f);

	return 0;
}