import sys

sys.setrecursionlimit(10 ** 8)

input = sys.stdin.readline


def main():
    N, K = [int(x) for x in input().split()]

    def sum_up_to_n(n):
        return n * (n + 1) // 2

    print(sum_up_to_n(N) / ((N + 1)))
    
    

if __name__ == '__main__':
    main()