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 CPP):

Solution:
#include<stdio.h> 

int main() { 
 double x[22], y[22], ans = 0; 
 int n = 0; 
 int l;
 while (scanf("%lf,%lf", &x[n], &y[n]) != -1) { 
  n++; 
 } 
 double s; 
 for (int i = 1; i < n; i++) { 
  s = (x[i] - x[0])*(y[(i + 1) % n] - y[0]) - (x[(i + 1) % n] - x[0])*(y[i] - y[0]); 
  if (s < 0)s = -s;
  ans += s;
 } 
 printf("%.8lf", ans/2.0); 
}