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:
ans=0
x,y=map(float,input().split(","))
k1,k2=map(float,input().split(","))
while 1:
    try:
        k3,k4=map(float,input().split(","))
        a=((k1-x)**2+(k2-y)**2)**0.5
        b=((k3-x)**2+(k4-y)**2)**0.5
        c=((k1-k3)**2+(k2-k4)**2)**0.5
        z=(a+b+c)/2
        ans+=(z*(z-a)*(z-b)*(z-c))**0.5
        k1,k2=k3,k4
    except:break
print(ans)