S(n)=sqrt (2+sqrt (2+sqrt (2+ sqrt (2+.............sqrt(2)).

/* Tinh S(n)=sqrt (2+sqrt (2+sqrt (2+ sqrt (2+.............sqrt(2)).....)))
có n dau can.
*/
// Khai bao cac ham thu vien neu cos
#include<stdio.h>
#include<conio.h>
#include<math.h> // thu vien cho sqrt, abs,...
void main()
{
	int n;
	scanf("%d",&n);
	double s=0;
	for(int i=1;i<=n;i++)
	{
		s=sqrt(2+s);
	}
	printf("%.4lf\n",s);// Lay 4 chu so sau dau thap phan
}