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<cstdio>
#include<complex>
#include<vector>
#include<cmath>
using namespace std;
typedef complex<double> P;
vector<P> coor;
double calarea();
double divtri(int i, int j);

int main(){
    double tmpx, tmpy;
    while(scanf("%lf,%lf", &tmpx, &tmpy) != EOF){
        coor.push_back(P(tmpx, tmpy));
    }
    printf("%f\n", calarea());
    return 0;
}

double calarea(){
    double ans = 0;
    for(int i = 0; i < coor.size() - 1; i++){
        ans += divtri(i, i + 1);
    }
    ans += divtri(coor.size() - 1, 0);
    return ans;
}

double divtri(int i, int j){
    return abs(imag(conj(coor[i]) * coor[j])) / 2;
}