How do I simplify big Numbers?

my game uses really big number and i need to simplify them somehow with some king of decimals like

for 1.400.000 it will be 1.40 Mil

for 23.539.520 ---- 23.53 Mil

for 12.423.414.123 --- 12.42 Bil

something like this

someone knows how to do it ?

Thanks <3

EDIT : or something that let you pick a certain number of decimals.