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 <stdio.h>
#include <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;

xy_t P[110];
double cross_product(xy_t a,xy_t b);

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) != EOF) {
    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];
    sum += abs(cross_product(b-a,c-a)/2.0);
  }
  printf("%.6f\n", abs(sum));
}

double cross_product(xy_t a,xy_t b) {
  return (conj(a)*b).imag();
}