#include<set>
#include<map>
#include<queue>
#include<stack>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include <iomanip>
#include<algorithm>
#define RG register int
#define rep(i,a,b)    for(RG i=a;i<=b;++i)
#define per(i,a,b)    for(RG i=a;i>=b;--i)
#define ll long long
#define inf (1<<29)
#define maxn 1005
#define eps 1e-8
using namespace std;
int n;
double a,ans=1e20;
double H[maxn];
inline int read()
{
	int x=0,f=1;char c=getchar();
	while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
	while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
	return x*f;
}

int check(double b)
{
	double A=a,B=b,C;
	rep(i,3,n)
	{
		C=2.0*B+2.0-A;
		if(C<0)	return 0;
		A=B,B=C;
	}
	ans=min(ans,C);
	return 1;
}

int main()
{
	n=read();scanf("%lf",&a);
	double l=-1,r=1030,mid;
	while(r-l>eps)
	{
		mid=(l+r)/2;
		if(check(mid))	r=mid;
		else			l=mid;
	}
	printf("%.2f",ans);//printf("%.2lf",ans);waaaaa?
	return 0;
}