from math import atan,sin,cos
xs,ys,xf,yf = [int(i) for i in input().split()]
n = int(input())

minim = "a"
maxim = "a"
d = []
for i in range(n):
    o = [int(k) for k in input().split()]
    d.append(o)
if ys == yf:
    e = 1
elif xs == xf:
    e = 0
else:
    e = 0
    tg = (yf-ys)/(xf-xs)
    for i in range(n):
        x = d[i][0]
        d[i][0] = d[i][0]*cos(atan(tg)) - d[i][1]*sin(atan(tg))
        d[i][1] = x*sin(atan(tg)) + d[i][1]*cos(atan(tg))
for i in range(n):
    o = d[i]
    r = o[2]
    y = o[e]
    if minim == "a":
        minim = y-r
    if minim > y-r:
        minim = y-r
    if maxim == "a":
        maxim = y+r
    if maxim < y+r:
         maxim = y+r

d.sort(key=lambda o:o[e])
pr = [minim]
for i in range(n):
    o = d[i]
    y = o[e]
    r = o[2]

    if i != 0:
        opred = d[i-1]
        ypred = opred[e]
        rpred = opred[2]
        if y-r > ypred+rpred or y-r <= ypred-rpred:
            pr.append(y-r)
    if i != n-1:
        oposl = d[i-1]
        yposl = oposl[e]
        rposl = oposl[2]
        if y+r < yposl-rposl or y+r >= yposl+rposl:
            pr.append(y+r)
pr.append(maxim)
pr = sorted(list(set(pr)))

res = 0
for i in range(len(pr)-1):
    if i % 2 == 1:
        if pr[i+1] - pr[i] > res:
            res = pr[i+1]-pr[i]

print(res)