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 get_input():
    while True:
        try:
            yield ''.join(input())
        except EOFError:
            break

N = list(get_input())
x0,y0 = [float(i) for i in N[0].split(",")]
ans = 0.0
for l in range(2,len(N)):
    x1, y1 = [float(i) for i in N[l-1].split(",")]
    x2, y2 = [float(i) for i in N[l].split(",")]
    a = math.sqrt((x1-x0)**2 + (y1-y0)**2)
    b = math.sqrt((x2-x1)**2 + (y2-y1)**2)
    c = math.sqrt((x2-x0)**2 + (y2-y0)**2)
    z = (a+b+c)/2.0
    S = math.sqrt(z*(z-a)*(z-b)*(z-c))
    ans += S
print(ans)