# -*- coding: utf-8 -*-

import math

def main():
    C = float(input())
    Rin, Rout = map(float, input().split())

    # V=1/4pi^2*(r+R)(R-r)^2
    cal=0.25*((math.pi*(Rout-Rin))**2)*(Rout+Rin)*C
    print(u'%.10f'%cal)

if __name__ == '__main__':
    main()