import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

c = I()
ri, ro = MI()

r = (ro-ri)/2
r2 = (ro+ri)/2
ans = r**2*math.pi*2*r2*math.pi*c

print(ans)