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 <map>
#include <cmath>
using namespace std;

int main(){
  pair<double,double> p[20];
  int i=1;
  double a,b,c,z,S;
  S=0.0;
  scanf("%lf,%lf",&p[0].first,&p[0].second);
  scanf("%lf,%lf",&p[1].first,&p[1].second);
  while(scanf("%lf,%lf",&p[i+1].first,&p[i+1].second)>0){
    a=sqrt((p[i+1].first-p[0].first)*(p[i+1].first-p[0].first)+(p[i+1].second-p[0].second)*(p[i+1].second-p[0].second));
    b=sqrt((p[i].first-p[0].first)*(p[i].first-p[0].first)+(p[i].second-p[0].second)*(p[i].second-p[0].second));
    c=sqrt((p[i].first-p[i+1].first)*(p[i].first-p[i+1].first)+(p[i].second-p[i+1].second)*(p[i].second-p[i+1].second));
    z=(a+b+c)/2;
    S+=sqrt(z*(z-a)*(z-b)*(z-c));
    i++;
  }
  printf("%.6lf\n",S);
return 0;
}