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
x, y, r, l, s = [], [], [], [], []
while True:
    try:
        a, b = map(float, raw_input().split(","))
        x.append(a); y.append(b)
    except:
        break
    
for i in range(len(x)-1):
    r.append(math.sqrt((x[i+1] - x[0])**2 + (y[i+1] - y[0])**2))
for i in range(1,len(x)-1):
    l.append(math.sqrt((x[i+1] - x[i])**2 + (y[i+1] - y[i])**2))
for i in range(len(x)-2):
    s.append((r[i]+r[i+1]+l[i])/2)

sum = 0.0
for i in range(len(x)-2):
    sum += math.sqrt(s[i]*(s[i]-r[i])*(s[i]-r[i+1])*(s[i]-l[i]))
    
print sum