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 <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;

struct Point{
  double x, y;
};

int main(){
  int n;
  Point P[21];
  int cs = 0;
  while(scanf("%lf,%lf", &P[cs].x, &P[cs].y) != EOF){
    cs++;
  }
  
  double area = 0;
  
  for(int i = 0 ; i < cs-1 ; i++){
    area += P[i].x * P[i+1].y - P[i].y * P[i+1].x;
  }
  area += P[cs-1].x * P[0].y - P[cs-1].y * P[0].x;
  
  printf("%f\n", abs(area)/2);
  return 0;
}