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 <bits/stdc++.h>
using namespace std;
int main(){
  double x[25],y[25],ans=0,a,b,c,z;
  int cnt=0;
  while(scanf("%lf,%lf",&x[cnt],&y[cnt])!=EOF){
    if(cnt>=2){
      a=sqrt(fabs(x[0]-x[cnt-1])*fabs(x[0]-x[cnt-1])+fabs(y[0]-y[cnt-1])*fabs(y[0]-y[cnt-1]));
      b=sqrt(fabs(x[cnt-1]-x[cnt])*fabs(x[cnt-1]-x[cnt])+fabs(y[cnt-1]-y[cnt])*fabs(y[cnt-1]-y[cnt]));
      c=sqrt(fabs(x[cnt]-x[0])*fabs(x[cnt]-x[0])+fabs(y[cnt]-y[0])*fabs(y[cnt]-y[0]));
      z=(a+b+c)/2.0;
      ans+=sqrt(z*(z-a)*(z-b)*(z-c));
    }
    cnt++;
  }
  printf("%.10lf\n",ans);
  return 0;
}