description: You are given two integers l and r, l≤ r. Find the largest possible value of a mod b over all pairs (a, b) of integers for which r≥ a ≥ b ≥ l.
  
  As a reminder, a mod b is a remainder we get when dividing a by b. For example, 26 mod 8 = 2.
  
  Input
  
  Each test contains multiple test cases.
  
  The first line contains one positive integer t (1≤ t≤ 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≤ l ≤ r ≤ 10^9).
  
  Output
  
  For every test case, output the largest possible value of a mod b over all pairs (a, b) of integers for which r≥ a ≥ b ≥ l.
  
  Example
  
  Input
  
  
  4
  1 1
  999999999 1000000000
  8 26
  1 999999999
  
  
  Output
  
  
  0
  1
  12
  499999999
  
  Note
  
  In the first test case, the only allowed pair is (a, b) = (1, 1), for which a mod b = 1 mod 1 = 0.
  
  In the second test case, the optimal choice is pair (a, b) = (1000000000, 999999999), for which a mod b = 1.
solution: #include <bits/stdc++.h>
  using namespace std;
  void Pagla() {
    int i, j;
    long long int a, b;
    cin >> a >> b;
    if (a == b) {
      cout << 0 << "\n";
      return;
    }
    if (b - a == 1) {
      if (b % a == 0)
        cout << 0 << "\n";
      else
        cout << 1 << "\n";
      return;
    }
    if (b / 2 >= a) {
      long long int ak = ceil(b * 1.00 / 2);
      long long int mx = 0;
      mx = max(mx, b % ak);
      while (1) {
        if (b % ak != 0) {
          break;
        }
        mx = max(mx, b % ak);
        ak++;
        if (ak >= b) {
          cout << mx << "\n";
          return;
        }
      }
      cout << max(mx, b % ak) << "\n";
    } else {
      if (b % a != 0) {
        cout << b % a << "\n";
      } else {
        if (a != 1)
          cout << b % (a - 1) << "\n";
        else
          cout << b % a << "\n";
      }
    }
  }
  int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    t = 1;
    cin >> t;
    while (t--) {
      Pagla();
    }
    return 0;
  }
  