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
import cmath
def cross_product(a,b):
    return (a.conjugate()*b).imag
L = []
try:
    while True:
        x,y = map(float,input().split(','))
        L.append(complex(x,y))
except EOFError:
    pass
N = len(L)
S = 0
for i in range(1,N-1):
    a,b,c = L[0],L[i],L[i+1]
    S += abs(cross_product(b-a,c-a))/2
print(S)