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:
from math import sqrt
x = []
y = []
while(1):
    try:
        a = [float(i) for i in input().split(",")]
        x.append(a[0])
        y.append(a[1])
    except EOFError:
        break
n = len(x)
S = 0

for i in range(n-2):
    if i == 0:
        a = sqrt((x[1]- x[0])**2 + (y[1]-y[0])**2)
    b = sqrt((x[i+2]- x[i+1])**2 + (y[i+2]-y[i+1])**2)
    c = sqrt((x[i+2]- x[0])**2 + (y[i+2]-y[0])**2)
    z = (a+b+c)/2
    s = sqrt(z*(z-a)*(z-b)*(z-c))
    S = S + s
    a = c

print("{:.6f}".format(S))