Solve the programming task below in a Python markdown code block.
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You are given two integers $L$ and $R$. Find the smallest non-negative integer $N$ such that
$$N \,\%\, L > N \,\%\, (L + 1) > \ldots > N \,\%\, (R - 1) > N \,\%\, R \,.$$

Here, $\%$ is the modulo operator, so $A \,\%\, B$ is the remainder of $A$ after division by $B$. For example, $11 \,\%\, 3 = 2$.

------  Input ------
The first line of the input contains a single integer $T$ denoting the number of test cases. The description of $T$ test cases follows.
The first and only line of each test case contains two space-separated integers $L$ and $R$.

------  Output ------
For each test case, print a single line containing one integer ― the smallest possible $N$, or $-1$ if no solution exists.

It is guaranteed that when a solution exists, the smallest solution does not exceed $10^{18}$.

------  Constraints ------
$1 ≤ T ≤ 10^{5}$
$1 ≤ L < R ≤ 10^{6}$

----- Sample Input 1 ------ 
2

4 6

1 2
----- Sample Output 1 ------ 
6

-1
----- explanation 1 ------ 
Example case 1: $N = 6$ satisfies the given condition, since $6 \,\%\, 4 \,(= 2) > 6 \,\%\, 5 \,(= 1) > 6 \,\%\, 6 \,(= 0)$. Notice that $N = 7$ also satisfies the condition, but it is larger.

Example case 2: It is impossible to find a valid solution because for any non-negative integer $N$, we have $N \,\%\, 1 \,(= 0) ≤ N \,\%\, 2$.