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<iostream>
#include<iomanip>
#include<complex>
#include<cmath>
#include<cstdlib>
using namespace std;

typedef complex<double> xy_t;
xy_t P[21];

double heron(xy_t p,xy_t q,xy_t r){
    double a=abs(p-q),b=abs(q-r),c=abs(r-p);
    double z=(a+b+c)/2;
    return sqrt(z*(z-a)*(z-b)*(z-c));
}

int main(){
    double x,y;
    char noise;
    int n=0;

    while(cin>>x>>noise>>y){
        P[n++]=xy_t(x,y);
    }
    //i?????????????????°????????´??????????????????
    //cerr<<n<<"\n";

    double S=0.0;
    for(int i=0;i<n-2;++i){
        S+=heron(P[0],P[i+1],P[i+2]);
    }

    cout<<fixed<<setprecision(6)<<S<<"\n";
}