C = int(input())
R_in, R_out = list(map(int, input().split()))

danmen_r = (R_out - R_in) / 2
danmenseki = 3.14159265 * (danmen_r ** 2)

jiku = 2 * 3.14159265 * (R_out - danmen_r)

donut_cal = C * danmenseki * jiku

print(donut_cal)