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 <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
#define FOR(i,a,b) for(int i=(a);i<(int)(b);++i)
#define rep(i,n) FOR(i,0,n)

vector<double> x, y;

double __pow(double a) {
    return a * a;
}

int main() {
    double px,py;
    while(~scanf("%lf,%lf",&px,&py)) {
        x.push_back(px); y.push_back(py);
    }

    int n = x.size();
    double s = 0;
    FOR(i,2,n) {
        double a = sqrt(__pow(x[0]-x[i-1]) + __pow(y[0]-y[i-1]));
        double b = sqrt(__pow(x[0]-x[i]) + __pow(y[0]-y[i]));
        double c = sqrt(__pow(x[i-1]-x[i]) + __pow(y[i-1]-y[i]));
        double z = (a+b+c) / 2.0;
        s += sqrt(z * (z-a) * (z-b) * (z-c));
    }

    printf("%.15lf\n", s);

    return 0;
}