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 <vector>
#include <map>
#include <cmath>
using namespace std;

int main() {
  double x, y;
  vector<pair<double, double>> v;
    char c;
    while(cin >> x >> c >> y) v.push_back(make_pair(x,y));     

  double S = 0;
  for(int i = 1; i < v.size()-1; i++) {
    double x1 = v[0].first,   y1 = v[0].second;
    double x2 = v[i].first, y2 = v[i].second;
    double x3 = v[i+1].first, y3 = v[i+1].second;
  
    double a = hypot(x2-x1, y2-y1), b = hypot(x3-x2, y3-y2), c = hypot(x1-x3, y1-y3);
    double z = (a+b+c) / 2;
    S += sqrt(z * (z-a) * (z-b) * (z-c));
  }
  
  printf("%.6lf\n", S);
}