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<vector>
#include<queue>
#include<stack>
#include<map>
#include<string>
#include<algorithm>
#include<utility>
#include<math.h>
#include<iomanip>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
const int INF = pow(10, 8);
int main(){
  double ax, ay, bx, by, cx, cy;char c;
  cin>>ax>>c>>ay>>bx>>c>>by;
  double ans=0;
  while(cin>>cx>>c>>cy){
    double d1 = pow((pow(ax-bx, 2)+pow(ay-by, 2)), 0.5);
    double d2 = pow((pow(bx-cx, 2)+pow(by-cy, 2)), 0.5);
    double d3 = pow((pow(cx-ax, 2)+pow(cy-ay, 2)), 0.5);
    double z = (d1+d2+d3)*0.5;
    ans += pow((z*(z-d1)*(z-d2)*(z-d3)), 0.5);
    bx=cx;by=cy;
    // cout<<fixed<<setprecision(10)<<ans<<endl;
  }
  cout<<fixed<<setprecision(10)<<ans<<endl;
  return 0;
}