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 sys
f = sys.stdin

def triangle_area(a, b, c):
    z = (a + b + c) / 2
    s = (z * (z - a) * (z - b) * (z - c)) ** 0.5
    return s

apexes = []
for line in f:
    x, y = map(float, line.split(','))
    apexes.append(x + y * 1j)

s = 0
for i in range(2,len(apexes)):
    s += triangle_area(abs(apexes[0] - apexes[i - 1]),abs(apexes[0] - apexes[i]),abs(apexes[i] - apexes[i - 1]))
print(s)