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 <complex>
 #include <stdio.h>
 #include<cmath>
 using namespace std;
 typedef complex<double>xy_t;
 xy_t P[110];

 double cross_product(xy_t a, xy_t b) //??????
 { return (conj(a) * b).imag(); }

int main(){
    int n=0;
    double x,y,sum=0.0;
    while(scanf("%lf,%lf",&x,&y)!=EOF)
        {
            P[n++]=xy_t(x,y);
        }
    for(int i=0;i+2<n;i++)
        {
            xy_t a=P[0],b=P[i+1],c=P[i+2];
            sum+=cross_product(b-a,c-a);
        }
        cout<<sum/2<<endl;
 }