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 <iostream>
#include <algorithm>
#include <vector>
#include <math.h>
#include <cmath>
#include <utility>
#include <queue>
#include <stdio.h>
#include <string>
#include <map>
#include <stack>
#include <complex>
#define rep(i,n) for(int i=0;i<n;i++)
#define INF 1000000000007
using namespace std;
typedef long long int ll;
typedef complex<double> xy;

int main(){
    vector<xy> inp(21);
    double x,y;
    int n=0;
    string S;
    while (~scanf("%lf,%lf", &x, &y)) {
        inp[n++]=xy(x,y);
    }
    double ans=0.0;
    for (int i=1; i<n-1; i++) {
        xy a = inp[i], b = inp[i+1];
        xy hoge=a-inp[0],piyo=b-inp[0];
        ans += abs((conj(hoge)*piyo).imag())/2.0;
    }
    printf("%.6f\n", ans);
}