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 <cmath>
#include <complex>
#include <cstdio>
#include <iomanip>
#include <iostream>
#define FOR(i,k,n) for (int (i)=(k); (i)<(n); ++(i))
#define REP(i,n) FOR(i,0,n)

using namespace std;

typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b){ return (conj(a) * b).imag(); }

int main(){
    int n = 0;
    double x,y,area = 0;
    xy_t p[20];
    while(~scanf("%lf,%lf", &x, &y)){
        p[n] = xy_t(x, y);
        n++;
    }

    REP(i,n - 2){
        area += fabs(cross_product(p[i+1] - p[0], p[i+2] - p[0])) / 2;
    }
    cout << area << endl;

}