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:
# Aizu Problem 0079: Area of Polygon
#
import sys, math, os

# read input:
PYDEV = os.environ.get('PYDEV')
if PYDEV=="True":
    sys.stdin = open("sample-input.txt", "rt")


def poly_area(polygon, M):
    A = 0
    for i in range(M):
        x1, y1 = polygon[i][0], polygon[i][1]
        x2, y2 = polygon[(i+1)%M][0], polygon[(i+1)%M][1]
        A += (x1 * y2 - x2 * y1)
    return abs(A / 2)


poly = [[float(_) for _ in line.split(',')] for line in sys.stdin]
print("%.6f" % poly_area(poly, len(poly)))