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.

<image>



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 <complex>
#include <vector>
using namespace std;
typedef complex<double> P;

int main(){
    vector<P> ps;
    double x,y;
    while(~scanf("%lf,%lf\n",&x,&y)){
        ps.push_back(P(x,y));
    }
    double S=0;
    for(int i=1;i+1<ps.size();i++){
        S+=abs((conj(ps[i]-ps[0])*(ps[i+1]-ps[0])).imag())/2;
    }
    printf("%.8f\n",S);
}