def b():
    i = input()
    i2 = input()
    i2L = i2.split()
    i2L = [int(i) for i in i2L]
    count = 0
    s = 0
    for v in i2L:
        if v != -1:
            count += 1
            s += v
    print(s * 1.0 / count)


b()

3a055e6ecd890f13ab58950f717024820ef537b4
<mask token>

def b():
    i = input()
    i2 = input()
    i2L = i2.split()
    i2L = [int(i) for i in i2L]
    count = 0
    s = 0
    for v in i2L:
        if v != -1:
            count += 1
            s += v
    print(s * 1.0 / count)


<mask token>

def b():
    i = input()
    i2 = input()
    i2L = i2.split()
    i2L = [int(i) for i in i2L]
    count = 0
    s = 0
    for v in i2L:
        if v != -1:
            count += 1
            s += v
    print(s * 1.0 / count)


b()
