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 <complex>
#include <cmath>
#include <iostream>
using namespace std;

typedef complex<double> xy_t;
xy_t P[110];

int main() {
  //入力例　読み込んだ点の個数をNとする
  int N = 0;
  double x,y;
  while (~scanf("%lf,%lf", &x, &y)) {
    P[N++] = xy_t(x,y);
	}
	//面積計算
	double sum = 0.0;
	for (int i = 0; i+2 < N; ++i) {
	  xy_t a = P[0], b = P[i+1], c = P[i+2];
	  xy_t ab = P[i+1] - P[0], bc = P[i+2] - P[i+1], ca = P[0] - P[i+2];
	  double z = (abs(ab) + abs(bc) + abs(ca))/2;
	  double s = sqrt(z*(z-abs(ab))*(z-abs(bc))*(z-abs(ca)));
	  sum += s;
	  }
	printf("%.6f\n", abs(sum));
}

/* 自分のMac環境ではコンパイルも通り、正しい答えが出力されるのですがオンラインジャッジではコンパイルエラーになってしまいます。どうしてでしょうか? */