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

typedef complex<double> Point;

#define X real()
#define Y imag()

int n;
double ans;
Point ps[1000000];

double cross(Point a, Point b) {
  return (conj(a)*b).Y;
}

int main() {
  for (n=0; ; n++) {
    double x, y;
    if (scanf("%lf,%lf", &x, &y) != 2) break;
    ps[n] = Point(x, y);
  }

  for (int i=1; i<n-1; i++) {
    ans += abs(cross(ps[i+1]-ps[0], ps[i]-ps[0]));
  }

  printf("%f\n", ans/2);
}