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:
def solve():
    from sys import stdin
    lines = stdin
    
    x1, y1 = map(float, lines.readline().split(','))
    x2, y2 = map(float, lines.readline().split(','))
    
    vx1 = x2 - x1
    vy1 = y2 - y1
    
    area = 0
    for line in lines:
        x3, y3 = map(float, line.split(','))
        
        vx2 = x3 - x1
        vy2 = y3 - y1
        
        area += abs(vx1 * vy2 - vy1 * vx2) / 2
        
        vx1, vy1 = vx2, vy2
    
    print(area)

solve()