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 <cstdio>
#include <cmath>
#include <iostream>
using namespace std;
typedef double d;

d heron(d a,d b,d c){
  d s = (a+b+c)/2;
  return sqrt(s*(s - a)*(s - b)*(s - c));
}
int main(){
  d x1,y1,x2,y2,x3,y3;
  char c;
  d sum = 0.0;
  cin >> x1 >>c>> y1>> x2 >> c >> y2;
  while( cin >> x3 >> c >> y3){
    double a = sqrt(pow(x1 - x2,2) + pow(y1 - y2,2));
    double b = sqrt(pow(x1 - x3,2) + pow(y1 - y3,2));
    double c = sqrt(pow(x2 - x3,2) + pow(y2 - y3,2));
    sum +=  heron(a,b,c);
    x2 = x3,y2 = y3;
  }
  printf("%.6f\n",sum);
}