p00079 Area of Polygon
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
```python
i = 0
x = []
y = []
while 1:
    try:
        a,b = map(float,input().split(","))
        x.append(a)
        y.append(b)
    except EOFError:
        break

S = 0
for i in range(len(x)-2):
    a = ((x[0]-x[i+1]) ** 2 + (y[0]-y[i+1]) ** 2) ** 0.5
    b = ((x[0]-x[i+2]) ** 2 + (y[0]-y[i+2]) ** 2) ** 0.5
    c = ((x[i+1]-x[i+2]) ** 2 + (y[i+1]-y[i+2]) ** 2) ** 0.5
    z = (a + b + c)/2
    S += (z * (z - a) * (z - b) * (z - c)) ** 0.5
print(S)

```