# This code is written in the Julia language
# Function I wrote to Knuth shuffle an array!
function shuffle(x, length)
    i = 1
    while i < length
        j = i + rand(0:length - i)
        temp = x[i]
        x[i] = x[j]
        x[j] = temp
        i += 1
    end
    return x
end

# x = [1,2,3,4,5,6,7,8,9,10] # for the other version
x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
l = length(x)

trials = 100000000 

function hasSorD(x, length)
    i = 1
    while i <= length
        if x[i] == i
            return true
        end
        
        j = x[i]
        if x[j] == i
            return true
        end
        i += 1
    end
    return false
end

count = 0

i = 0

while i < trials
    x = shuffle(x, l)
    if (!hasSorD(x, l))
        count += 1
    end
    i += 1
end

print(count/trials)