How to find 1's complement in MARIE?

Question

I'm trying to write Checksum Algorithm using MARIE.js, but I'm stuck on doing 1's complement. I saw other assembly languages have CMA code, but I couldn't find that information on MARIE. Thus, I typed G that opcode is 2F to find the checksum byte but the output is not what I expected. What did I miss or do something wrong?

Input      /Takes user input
Store A    /Stores user input to A
Input      /Takes user input
Store B    /Stores user input to B
Input      /Takes user input
Store C    /Stores user input to C
Input      /Takes user input
Store D    /Stores user input to D

Load A     /Load A to AC
Add B      /Add B to A
Add C      /Add C to B
Add D      /Add D to C
Subt F     /Subtract F from Sum of data 1,2,3,4
Store E    /Sum of data 1,2,3,4 ignoring carry
Subt G
/Add ONE 
Output     /Print checksum byte
HALT       /End program

/Variable decleration
A, HEX 0 /Data 1
B, HEX 0 /Data 2
C, HEX 0 /Data 3
D, HEX 0 /Data 4
E, HEX 0 /Checksum byte
F, HEX 100 /Ignore carry
G, HEX 2F
ONE, DEC 1

Answer 1

Two's complement, -n, is defined as one's complement + 1, e.g. ~n + 1

Therefore, since MARIE has subtraction you can make two's complement (e.g. 0-n) and subtracting 1 from that will yield one's complement, ~n.