#include<stdio.h>
//Who can tell me why my programme is wrong? It seem to be so
//simple and I think is should be right.
#define Max(a,b) (a>b?a:b)

typedef long double type;

double N;
type H1,H2;

int main()
{ float a;
  type i;
 scanf("%lf %f",&N,&a); H1=(type)a; H2=0;
 for (i=2; i<=N; i++) H2=Max(H2,(H1*(i-2)-(i-1)*(i-2))/(i-1));
 printf("%0.2lf\n",(double)Max(0,H2*(N-1)-H1*(N-2)+(N-1)*(N-2)));
 return 0;
}