def decompress_amount(x):
    """\
    Undo the value compression performed by x=compress_amount(n). The input
    x matches one of the following patterns:
        x = n = 0
        x = 1+10*(9*n + d - 1) + e
        x = 1+10*(n - 1) + 9"""
    if not x: return 0;
    x = x - 1;

    # x = 10*(9*n + d - 1) + e
    x, e = divmod(x, 10);
    n = 0;
    if e < 9:
        # x = 9*n + d - 1
        x, d = divmod(x, 9)
        d = d + 1
        # x = n
        n = x*10 + d
    else:
        n = x + 1
    return n * 10**e