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 calc_d(a, b):
    return math.sqrt((a[0] - b[0])**2 + (a[1] - b[1])**2)

p = []
while True:
    try:
        p.append(list(map(float, input().split(","))))
    except:
        break

n = len(p)
s = 0
for i in range(1, n - 1):
    a = calc_d(p[0], p[i])
    b = calc_d(p[0], p[i+1])
    c = calc_d(p[i], p[i+1])
    z = (a + b + c)/2
    s += math.sqrt(z*(z - a)*(z - b)*(z - c))
print(s)