CF1366B Shuffle

You are given an array consisting of $ n $ integers $ a_1 $ , $ a_2 $ , ..., $ a_n $ . Initially $ a_x = 1 $ , all other elements are equal to $ 0 $ . You have to perform $ m $ operations. During the $ i $ -th operation, you choose two indices $ c $ and $ d $ such that $ l_i \le c, d \le r_i $ , and swap $ a_c $ and $ a_d $ . Calculate the number of indices $ k $ such that it is possible to choose the operations so that $ a_k = 1 $ in the end.

The first line contains a single integer $ t $ ( $ 1 \le t \le 100 $ ) — the number of test cases. Then the description of $ t $ testcases follow. The first line of each test case contains three integers $ n $ , $ x $ and $ m $ ( $ 1 \le n \le 10^9 $ ; $ 1 \le m \le 100 $ ; $ 1 \le x \le n $ ). Each of next $ m $ lines contains the descriptions of the operations; the $ i $ -th line contains two integers $ l_i $ and $ r_i $ ( $ 1 \le l_i \le r_i \le n $ ).

For each test case print one integer — the number of indices $ k $ such that it is possible to choose the operations so that $ a_k = 1 $ in the end.

In the first test case, it is possible to achieve $ a_k = 1 $ for every $ k $ . To do so, you may use the following operations: 1. swap $ a_k $ and $ a_4 $ ; 2. swap $ a_2 $ and $ a_2 $ ; 3. swap $ a_5 $ and $ a_5 $ . In the second test case, only $ k = 1 $ and $ k = 2 $ are possible answers. To achieve $ a_1 = 1 $ , you have to swap $ a_1 $ and $ a_1 $ during the second operation. To achieve $ a_2 = 1 $ , you have to swap $ a_1 $ and $ a_2 $ during the second operation.