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:
vertices = []
for _ in range(20):
    try:
        vertices.append([float(x) for x in input().split(',')])
    except:
        break
n = len(vertices)

def dist(p,q):
    return ((p[0]-q[0])**2 + (p[1]-q[1])**2)**0.5

def area(p,q,r):
    a = dist(p,q)
    b = dist(q,r)
    c = dist(r,p)
    z = (a+b+c)/2
    return (z*(z-a)*(z-b)*(z-c))**0.5

S = 0
for i in range(1,n-1):
    S += area(vertices[0],vertices[i],vertices[i+1])

print(S)