
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given a set $A=\{a_1,a_2,a_3,\ldots,a_n\}$, let $M(A)$ denote the number of distinct values among all sums $a_i+a_j$ ($1\leq i<j\leq n$). For example, when $A=\{1,2,3,4\}$, since $1+2=3$, $1+3=4$, $1+4=2+3=5$, $2+4=6$, $3+4=7$, we have $M(A)=5$. For a set $B=\{b_1,b_2,b_3,\ldots,b_n\}$, if the real numbers $b_1,b_2,b_3,\ldots,b_n$ form an arithmetic sequence, then $M(B)=\boxed{2n-3}$.

Present the answer in LaTex format: \boxed{Your answer}
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