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<math.h>
using namespace std;

double sq(double a){
    return a*a;
}
int main(){
    vector<pair<double,double> >vec;
    double x,y,b,z,s=0;
    char c;
    while(cin>>x>>c>>y)
        vec.push_back(make_pair(x, y));
    int a=1;
    while(a+1!=vec.size()){
        x=sqrt(sq(vec[0].first-vec[a].first)+sq(vec[0].second-vec[a].second));
        y=sqrt(sq(vec[0].first-vec[a+1].first)+sq(vec[0].second-vec[a+1].second));
        b=sqrt(sq(vec[a+1].first-vec[a].first)+sq(vec[a+1].second-vec[a].second));
        z=(x+y+b)/2;
        s+=sqrt(z*(z-x)*(z-b)*(z-y));
        a++;
    }
    cout<<s<<endl;
}