def bubblesort(seq):
    length = len(seq)
    for i in range(length):
        for j in range(1,length-i):
            if seq[j-1] > seq[j]:
                seq[j-1],seq[j] = seq[j],seq[j-1]
    return seq

seq = [5,4,6,7,2,1]
print (bubblesort(seq))