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<iostream>
#include<cmath>
#include<cstdio>
#include<map>
#define l(a,b,c,d) sqrt(pow(c-a,2)+pow(d-b,2))
#define KEI(s,a,b,c) sqrt(s*(s-a)*(s-b)*(s-c))
using namespace std;
int main(){
  int n=0;
  double x[20],y[20];
  double sum = 0.0,a,b,c,s;

  while(scanf("%lf,%lf",&x[n],&y[n])!=EOF) n++;
  for(int i=2;i<n;i++){
    a = l(x[0],y[0],x[i-1],y[i-1]);
    b = l(x[0],y[0],x[i],y[i]);
    c = l(x[i-1],y[i-1],x[i],y[i]);
    sum += KEI((a+b+c)/2,a,b,c);
  }
  printf("%.10f\n",sum);
}