Answer: 3775
65. Divide the 100 natural numbers $1,2,3, \cdots \cdots, 100$ into 50 groups arbitrarily, with each group containing two numbers. Now, take any one of the two numbers in each group as $a$, and the other as $b$, and substitute them into the algebraic expression $\frac{1}{2}(|a-b|+a+b)$ for calculation. After substituting all 50 groups, 50 values can be obtained. Find the maximum value of the sum of these 50 values. $\qquad$