n = int(input())

cows = []

for _ in range(n):
    cows.append(tuple(map(int, input().split())))

def test(tx, ty):
    dist = 0.0
    for x, y, r in cows:
        dist = max(((tx - x)**2 + (ty - y)**2)**.5 - r, dist)
    return dist

xmin = -1000
xmax = 1000
ymin = -1000
ymax = 1000
while (xmax - xmin) > 0.0000001 or (ymax - ymin) > 0.0000001:
    best_val = 10000
    best = None
    pxmin, pxmax, pymin, pymax = xmin, xmax, ymin, ymax
    xs = pxmax - pxmin
    ys = pymax - pymin
    for i in range(5):
        for j in range(5):
            px = pxmin + (pxmax - pxmin) / 4 * i
            py = pymin + (pymax - pymin) / 4 * j
            dst = test(px, py)
            if dst < best_val:
                best_val = dst
                best = (px, py)
    px, py = best
    xmin = max(xmin, px - xs / 4)
    xmax = min(xmax, px + xs / 4)
    ymin = max(ymin, py - ys / 4)
    ymax = min(ymax, py + ys / 4)

print(test(xmin, ymin))