output_description: Print the minimum possible duration of time Snuke is exposed to cosmic rays
  during the travel. The output is considered correct if the absolute or
  relative error is at most 10^{-9}.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      x_s y_s x_t y_t
      N
      x_1 y_1 r_1
      x_2 y_2 r_2
      :
      x_N y_N r_N
attempt: xs, ys, xe, ye = map(int, input().split())
  n = int(input())
  xyr = [tuple(map(int, input().split())) for _ in range(n)]
  xyr.append((xs, ys, 0))
  xyr.append((xe, ye, 0))
  d = [[0] * (n + 2) for _ in range(n + 2)]
  for i in range(n + 1):
      for j in range(i + 1, n + 2):
          x, y, r = xyr[i]
          nx, ny, nr = xyr[j]
          tmp = ((x - nx) ** 2 + (y - ny) ** 2) ** 0.5
          tmp -= r + nr
          tmp = max(tmp, 0)
          d[i][j] = tmp
          d[j][i] = tmp
  
  
  inf = float("inf")
  seen = [inf] * (n + 2)
  seen[-2] = 0
  mi = set(range(n + 2))
  # n->n+1
  while mi:
      min_idx = 0
      min_d = inf
      for v in mi:
          if min_d > seen[v]:
              min_d = seen[v]
              min_idx = v
      v = min_idx
      mi.discard(v)
      if v == n + 1:
          break
      for nv in mi:
          seen[nv] = min(seen[nv], seen[v] + d[v][nv])
  print(seen[-1])
  
problem_description: Statement
  
  On the xy-plane, Snuke is going to travel from the point (x_s, y_s) to the
  point (x_t, y_t). He can move in arbitrary directions with speed 1. Here, we
  will consider him as a point without size.
  
  There are N circular barriers deployed on the plane. The center and the radius
  of the i-th barrier are (x_i, y_i) and r_i, respectively. The barriers may
  overlap or contain each other.
  
  A point on the plane is exposed to cosmic rays if the point is not within any
  of the barriers.
  
  Snuke wants to avoid exposure to cosmic rays as much as possible during the
  travel. Find the minimum possible duration of time he is exposed to cosmic
  rays during the travel.
samples: [{"input": "-2 -2 2 2\n    1\n    0 0 1", "output": "3.6568542495\n    \n\nAn optimal route is as follows:\n\n![e9c630751968b7051df5750b7ddc0e07.png](https://atcoder.jp/img/arc064/e9c630751968b7051df5750b7ddc0e07.png)\n\n* * *"}, {"input": "-2 0 2 0\n    2\n    -1 0 2\n    1 0 2", "output": "0.0000000000\n    \n\nAn optimal route is as follows:\n\n![fb82f6f4df5b22cffb868ce6333277aa.png](https://atcoder.jp/img/arc064/fb82f6f4df5b22cffb868ce6333277aa.png)\n\n* * *"}, {"input": "4 -2 -2 4\n    3\n    0 0 2\n    4 0 1\n    0 4 1", "output": "4.0000000000\n    \n\nAn optimal route is as follows:\n\n![d09006720c225cbe69eae3fd9c186e67.png](https://atcoder.jp/img/arc064/d09006720c225cbe69eae3fd9c186e67.png)"}]