import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
import numpy as np
def main():
    n, k = map(int, input().split())
    p = np.array(read().split(), np.int32)
    p += 1
    pcum = np.zeros(n + 1, np.int32)
    pcum[1:] = p.cumsum()
    sum_k = pcum[k:] - pcum[:-k]
    print(sum_k.max()/2)

if __name__ == '__main__':
    main() import sys sys read = sys.stdin.read read sys.stdin.read sys.stdin sys stdin read readlines = sys.stdin.readlines readlines sys.stdin.readlines sys.stdin sys stdin readlines import numpy as np numpy def main():
    n, k = map(int, input().split())
    p = np.array(read().split(), np.int32)
    p += 1
    pcum = np.zeros(n + 1, np.int32)
    pcum[1:] = p.cumsum()
    sum_k = pcum[k:] - pcum[:-k]
    print(sum_k.max()/2) main n, k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k p = np.array(read().split(), np.int32) p np.array(read().split(), np.int32) np.array np array read().split() ().split () read split np.int32 np int32 p += 1 p 1 pcum = np.zeros(n + 1, np.int32) pcum np.zeros(n + 1, np.int32) np.zeros np zeros n + 1 n 1 np.int32 np int32 pcum[1:] = p.cumsum() pcum[1:] pcum 1: 1 p.cumsum() p.cumsum p cumsum sum_k = pcum[k:] - pcum[:-k] sum_k pcum[k:] - pcum[:-k] pcum[k:] pcum k: k pcum[:-k] pcum :-k -k k print(sum_k.max()/2) print sum_k.max()/2 sum_k.max() sum_k.max sum_k max 2 if __name__ == '__main__':
    main() __name__ == '__main__' __name__ '__main__' main() main def main():
    n, k = map(int, input().split())
    p = np.array(read().split(), np.int32)
    p += 1
    pcum = np.zeros(n + 1, np.int32)
    pcum[1:] = p.cumsum()
    sum_k = pcum[k:] - pcum[:-k]
    print(sum_k.max()/2) def main():
    n, k = map(int, input().split())
    p = np.array(read().split(), np.int32)
    p += 1
    pcum = np.zeros(n + 1, np.int32)
    pcum[1:] = p.cumsum()
    sum_k = pcum[k:] - pcum[:-k]
    print(sum_k.max()/2) main read = sys.stdin.read sys.stdin.read read readlines = sys.stdin.readlines sys.stdin.readlines readlines
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
import numpy as np
def main():
    n, k = map(int, input().split())
    p = np.array(read().split(), np.int32)
    p += 1
    pcum = np.zeros(n + 1, np.int32)
    pcum[1:] = p.cumsum()
    sum_k = pcum[k:] - pcum[:-k]
    print(sum_k.max()/2)

if __name__ == '__main__':
    main()
