codechef obstacle course

import sys
import math
def main():
    answers =[]
    test_cases = int(raw_input())
    for i in range(test_cases):
        raw_input()
        dist = []
        radii = raw_input().split(' ')
        r = int(radii[0])
        R = int(radii[1])
        no_of_cones = int(raw_input())
        for j in range(no_of_cones):
            pos = raw_input().split(' ')
            x = int(pos[0])
            y = int(pos[1])
            d = math.sqrt(x*x+y*y)
            dist.append(max(R-d,d-r))
        answers.append(min(dist))
    for answer in answers: print '%.3f' % answer

main()