The problem is the '\n' character that follows your integer. When you call nextInt, the scanner reads the int, but it does not consume the '\n' character after it; nextLine does that. That is why you get an empty line instead of the string that you were expecting to get.
Let's say your input has the following data:
12345
hello
Here is how the input buffer looks initially (^ represents the position at which the Scanner reads the next piece of data):
1 2 3 4 5 \n h e l l o \n
^
After nextInt, the buffer looks like this:
1 2 3 4 5 \n h e l l o \n
^
The first nextLine consumes the \n, leaving your buffer like this:
1 2 3 4 5 \n h e l l o \n
^
Now the nextLine call will produce the expected result. Therefore, to fix your program, all you need is to add another call to nextLine after nextInt, and discard its result:
k = in.nextInt();
in.nextLine(); // Discard '\n'
input = in.nextLine();
