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 int ll;
const int INF = 1000000000;
#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)
#define rep(i,n) REP(i, 0, n)

typedef complex<double> Point;
double cross(const Point& a, const Point& b){
    return (conj(a) * b).imag();
}
int main() {
    vector<Point> poly;
    double x_, y_;
    char gomi;
    cin.tie(0); ios::sync_with_stdio(false);
    while(cin >> x_ >> gomi >>  y_) poly.push_back(Point(x_, y_));
//    rep(i, 5) {
//      cin >> x_ >> gomi >>  y_;
//      poly.push_back(Point(x_, y_));}
    double sum = 0.0;
    REP(i, 1, poly.size() - 1)
      sum += cross(poly[i] - poly[0], poly[i + 1] - poly[0]) / 2.0;
    cout << fixed << setprecision(10) << abs(sum) << endl;
    return 0;
}