Problem: Write a program that reads the coordinates of the vertices of a convex n-sided polygon (a polygon whose internal angles are less than 180 degrees, that is, a polygon that is not dented) and outputs its area. The vertices are named Vertex 1, Vertex 2, Vertex 3, ... Vertex n according to the order of edge connections.

However, n is 3 or more and 20 or less. You can also use the following formula to find the area S from the lengths a, b, and c of the three sides of the triangle.

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input

The input is given in the following format:


x1, y1
x2, y2
::
xn, yn


xi and yi are real numbers that represent the x and y coordinates of vertex i, respectively.

output

Outputs the area S (real number) on one line. The output can contain an error of 0.000001 or less.

Example

Input

0.0,0.0
0.0,1.0
1.0,1.0
2.0,0.0
1.0,-1.0


Output

2.500000

Solution (in PYTHON3):

Solution:
xlst = []
ylst = []
while True:
  try:
    x, y = map(float, input().split(","))
    xlst.append(x)
    ylst.append(y)
  except EOFError:
    break

num = len(xlst)
cx, cy = sum(xlst) / num, sum(ylst) / num

xlst.append(xlst[0])
ylst.append(ylst[0])
ans = 0
for i in range(num):
  x1, y1, x2, y2 = xlst[i], ylst[i], xlst[i + 1], ylst[i + 1]
  a = ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** (1 / 2)
  b = ((x1 - cx) ** 2 + (y1 - cy) ** 2) ** (1 / 2)
  c = ((x2 - cx) ** 2 + (y2 - cy) ** 2) ** (1 / 2)
  z = (a + b + c) / 2
  s = (z * (z - a) * (z - b) * (z - c)) ** (1 / 2)
  ans += s 
print(ans)