import math


def main():
    c = int(input())
    ri, ro = map(int, input().split())
    r1 = (ro + ri) / 2
    r2 = (ro - ri) / 2
    print(2 * math.pi ** 2 * r1 * r2 ** 2 * c)
    
    
if __name__ == '__main__':
    main()