what is the best way to enter amounts to variable with hotkeys?

[handlingcfg]

hi everyone,

im working on amount changer code for ut99, same code reads about 250 adresses, i need to enter two variable
what i want is pressing hotkeys and numbers to enter arbitrary amount to variable inside my code without exit fullscreen

example
while pressing some arbitrary keys like ctrl+f1 and i want to enter numbers like normal, for 15481 i press 1 - 5 - 4 -8 - 1 sequentally, then my variable turns 15481

right now i can write assembly code for this but it needs at least 15 hotkey and 1 for reset

1 select a variable x and change it with pressed number
2 press another button to add the variable x to y then multiply y with 10
3 repeat

this approach has another problem with multiple activation with hotkey, either it needs timer or another hotkey for prevent this

is there a better way?