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.

<image>



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:
# -*- coding: utf-8 -*-
'''
所要時間は、分位であった。
'''


# ライブラリのインポート
#import re
import sys
input = sys.stdin.readline
#import heapq
#import bisect
#from collections import deque
#import math

def main():
    P = []
    for line in sys.stdin:
        x, y = map(float, line.strip().split(','))
        P.append(complex(x, y))
    ans = areap(P)
    print(abs(ans))

def areap(P):
    s = 0
    n = len(P)
    for i in range(1,n-1):
        a, b, c = P[0],P[i],P[i+1]
        s += cdot(b-a,c-a)
    return s/2

def cdot(x, y):
    return (x.conjugate() * y).imag

    


    
if __name__ == '__main__':
    main()