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 <complex>
#include <cmath>
#include <iostream>
#include <stdio.h>
#include <cassert>

using namespace std;

typedef complex<double> xy_t;
xy_t P[110];
char c;
double x,y ;
int N = 0 ;
double s = 0.0;

int main() {
    // ??\???
    while(cin >> x >> c >> y){
        P[N] = xy_t(x,y);
        N++ ;
    }
    //?¨????
    for (int i=0; i+2<N; ++i){
        xy_t a = P[i+1] - P[0];
        xy_t b = P[i+2] - P[0];
        s = s + (conj(a)*b).imag()/2 ;
    }
    printf("%.6f\n", abs(s)) ;
}