CF1562A The Miracle and the Sleeper

You are given two integers $ l $ and $ r $ , $ l\le r $ . Find the largest possible value of $ a \bmod b $ over all pairs $ (a, b) $ of integers for which $ r\ge a \ge b \ge l $ . As a reminder, $ a \bmod b $ is a remainder we get when dividing $ a $ by $ b $ . For example, $ 26 \bmod 8 = 2 $ .

Each test contains multiple test cases. The first line contains one positive integer $ t $ $ (1\le t\le 10^4) $ , denoting the number of test cases. Description of the test cases follows. The only line of each test case contains two integers $ l $ , $ r $ ( $ 1\le l \le r \le 10^9 $ ).

For every test case, output the largest possible value of $ a \bmod b $ over all pairs $ (a, b) $ of integers for which $ r\ge a \ge b \ge l $ .

In the first test case, the only allowed pair is $ (a, b) = (1, 1) $ , for which $ a \bmod b = 1 \bmod 1 = 0 $ . In the second test case, the optimal choice is pair $ (a, b) = (1000000000, 999999999) $ , for which $ a \bmod b = 1 $ .