import sequtils,strutils,math
var
    c : float64 = stdin.readline.parsefloat
    R1,R2,R,r,V : float64
(R1, R2) = stdin.readline.split.map(parsefloat)
R = (R1 + R2) / 2
r = R - R1

proc F_out(x : float64): float64 =
    var d = r * r - x * x
    if d > 0:
        result = pow(R + sqrt(d), 2)
    else:
        result = 0
        
proc F_in(x : float64): float64 =
    var d = r * r - x * x
    if d > 0:
        result = pow(R - sqrt(d), 2)
    else:
        result = 0

proc integral(f : proc(x : float64) : float64 ; a : float64, b : float64): float64 =
    var
        n = a
        s : float64 = 0
        dx : float64 = 0.00001
    while n < b:
        s += f(n + dx / 2) * dx
        n += dx
    return s
        
V = PI * 2 * (integral(F_out, 0, r) - integral(F_in, 0, r))
echo V * c