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:
import math
f = []
while True:
    try:
        st = input().strip().split(',')
        x,y = list(map(float,st ))
        f.append(x + y*1j)
    except EOFError:
        break

ss = 0.0
fo = f[0]
for j in range(2,len(f)):
    i = j - 1
    a = abs(f[i]-fo)
    b = abs(f[j]-fo)
    c = abs(f[j]-f[i])
    z = (a + b + c) / 2.0
    s = math.sqrt(z*(z-a)*(z-b)*(z-c))
    ss += s
print("%.6f" % ss)