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:
# -*- coding: utf-8 -*-

import sys
import os
import math

def length(v, w):
    x_diff = v[0] - w[0]
    y_diff = v[1] - w[1]
    return math.sqrt(x_diff ** 2 + y_diff ** 2)

X = []
Y = []
for s in sys.stdin:
    x, y = map(float, s.split(','))
    X.append(x)
    Y.append(y)

n = len(X)
answer = 0
for i in range(1, n-1):
    p0 = (X[0], Y[0])
    p1 = (X[i], Y[i])
    p2 = (X[i+1], Y[i+1])

    a = length(p0, p1)
    b = length(p1, p2)
    c = length(p2, p0)

    z = (a + b + c) / 2
    S = math.sqrt(z * (z - a) * (z - b) * (z - c))
    answer += S
print(answer)