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 PYTHON):

Solution:
import math

def euclid_dis(c,d,a=0.0,b=0.0):
    return math.sqrt((c-a)**2.0+(d-b)**2.0)

def heron(a,b,c):
    z=(a+b+c)/2.0
    return math.sqrt(z*(z-a)*(z-b)*(z-c))

ans=0
xy=[]
while 1:
    try:
        xy.append(map(float,raw_input().split(",")))
    except:
        break

n=len(xy)

for i in xrange(2,n):
    a=euclid_dis(xy[(i-1)%n][0],xy[(i-1)%n][1],xy[0][0],xy[0][1])
    b=euclid_dis(xy[i%n][0],xy[i%n][1],xy[0][0],xy[0][1])
    c=euclid_dis(xy[i%n][0],xy[i%n][1],xy[(i-1)%n][0],xy[(i-1)%n][1])   
    ans+=heron(a,b,c)
print ans