How can I create a new dataframe if the input looks like this:

inputTable = pd.DataFrame({
    'A' : [1, 2, 3, 4, 5],
    'B' : [2, 3, 4, 5, 6],
    'C' : [3, 4, 5, 6, 7]
})

and the resulting table should look like this:

resultingTable = pd.DataFrame({
    'Category' : ['A', 'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', 'B', 'C', 'C', 'C', 'C', 'C'], 
    'Value'    : [1, 2, 3, 4, 5, 2, 3, 4, 5, 6, 3, 4, 5, 6, 7]
})

I am aware of pd.wide_to_long() but it seems to be an overkill for the simple case I am dealing with. Is there something more appropriate and, perhaps, more efficient?