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
X = []
Y = []

def area(a,b,c):
    p = math.sqrt((X [a] - X [b]) ** 2 + (Y [a] - Y [b]) ** 2)
    q = math.sqrt((X [b] - X [c]) ** 2 + (Y [b] - Y [c]) ** 2)
    r = math.sqrt((X [c] - X [a]) ** 2 + (Y [c] - Y [a]) ** 2)
    z = (p + q + r) / 2
    return math.sqrt(z * (z - p) * (z - q) * (z - r))

while True:
    try:
        a,b = map(float,input().split(','))
        X.append(a)
        Y.append(b)
    except EOFError:
        break

ans = 0.0
for i in range(1,len(X) - 1):
    ans += area(0,i,i + 1)
print(ans)