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:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
from __future__ import (division, absolute_import, print_function,
                        unicode_literals)
from sys import stdin
from math import hypot, sqrt

vertexs = []
for line in stdin:
    vertexs.append(tuple(float(s) for s in line.split(',')))

s = 0.0
x0, y0 = vertexs[0]
for i in range(1, len(vertexs)-1):
    x1, y1 = vertexs[i]
    x2, y2 = vertexs[i+1]

    a = hypot(x0 - x1, y0 - y1)
    b = hypot(x1 - x2, y1 - y2)
    c = hypot(x2 - x0, y2 - y0)
    z = (a + b + c) / 2.0
    s += sqrt(z * (z-a) * (z-b) * (z-c))
print('{:.6f}'.format(s))