import math

n, r = map(int, input().split())
if r * 2 <= n:
    print(math.pi * r * r)
    exit(0)
if 2 * r >= n * math.sqrt(2):
    print(n * n)
    exit(0)
print(math.pi * r * r - 4 * math.acos(n / r / 2)
      * r * r + 2 * n * math.sqrt(r * r - n * n / 4))