import std.stdio;
import std.string;
import std.conv;
import std.regex;

string text = "#Header
my header text

##SubHeader
my sub header text

###Sub3Header
my sub 3 text

###Sub31Header
my sub 3 text

#Header21
my header2 text

##SubHeader21
my header2 text

###SubHeader22
my header3 text
";

int main(string[] args)
{
    auto re = ctRegex!(`^(#+).+?$.+?(?:(?=^#)|$(?!.))`, "ms");

    int[] nums;
    foreach (m; text.matchAll(re))
    {
        auto len = m[1].length;

        while (nums.length && nums[$ - 1] >= len)
        {
            writeln("</div ", nums[$ - 1], ">");
            nums = nums[0..$ - 1];
        }

        nums ~= len.to!int;

        writeln("<div ", len, ">");
        writeln(m[0]);
    }

    foreach_reverse (len; nums)
    {
        writeln("</div ", len, ">");
    }

    return 0;
}