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
def angle(i1, j1, i2, j2, i3, j3) :
    a = math.sqrt((i1-i2)**2 + (j1-j2)**2)
    b = math.sqrt((i2-i3)**2 + (j2-j3)**2)
    c = math.sqrt((i3-i1)**2 + (j3-j1)**2)
    z = (a+b+c) / 2
    S = math.sqrt(z * (z-a) * (z-b) * (z-c))
    return S

ans = 0
x1, y1 = map(float, input().split(","))
x2, y2 = map(float, input().split(","))
while True :
    try :
        x3, y3 = map(float, input().split(","))
    except EOFError :
        break
    
    ans += angle(x1, y1, x2, y2, x3, y3)
    x2 = x3
    y2 = y3
    
print('{:.6f}'.format(ans))