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<cstdio>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
double x[32],y[32];
double heron(int cn);
int main(){
    int cnt = 0;
    while(~scanf("%lf,%lf",&x[cnt],&y[cnt])){
        cnt++;
    }
    double ans = 0.0;
    for(int q = 0;q < cnt-2; q++){
        ans += heron(q+1);
    }
    printf("%.6lf\n",ans);
    return 0;
}
double heron(int cn){
    double ab,ac,bc;
    ab = sqrt((x[0]-x[cn])*(x[0]-x[cn]) + (y[0]-y[cn])*(y[0]-y[cn]));
    ac = sqrt((x[0]-x[cn+1])*(x[0]-x[cn+1]) + (y[0]-y[cn+1])*(y[0]-y[cn+1]));
    bc = sqrt((x[cn]-x[cn+1])*(x[cn]-x[cn+1]) + (y[cn]-y[cn+1])*(y[cn]-y[cn+1]));

    double s=0,S=0;
    s = (ab+ac+bc)/2.0;
    S = sqrt(s*(s-ab)*(s-ac)*(s-bc));
    return S;
}