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: import sys
  import math
  import bisect
  from sys import stdin,stdout
  from math import gcd,floor,sqrt,log
  from collections import defaultdict as dd
  from bisect import bisect_left as bl,bisect_right as br
  
  sys.setrecursionlimit(100000000)
  input = sys.stdin.buffer.readline
  
  inp    =lambda: int(input())
  strng  =lambda: input().strip()
  jn     =lambda x,l: x.join(map(str,l))
  strl   =lambda: list(input().strip())
  mul    =lambda: map(int,input().strip().split())
  mulf   =lambda: map(float,input().strip().split())
  seq    =lambda: list(map(int,input().strip().split()))
  seq_nll    =lambda: list(map(int,input().strip()))
  
  ceil   =lambda x: int(x) if(x==int(x)) else int(x)+1
  ceildiv=lambda x,d: x//d if(x%d==0) else x//d+1
  
  flush  =lambda: stdout.flush()
  stdstr =lambda: stdin.readline()
  stdint =lambda: int(stdin.readline())
  stdpr  =lambda x: stdout.write(str(x))
  
  mod=1000000007
  
  
  #main code
  
  # vijayantyadav11
  
  for _ in range(int(input())):
      l,r=input().split()
      l=int(l)
      r=int(r)
      hf = r//2
      if hf==0:
          print(r%l)
      elif l<=hf:
          if r%(hf)==0:
              print(r%(hf+1))
          else:
              print(hf)
      else:
          print(r%l)