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 <cstdio>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <utility>
#include <bitset>
#include <climits>
#include <cassert>

using namespace std;
typedef long long ll;

int main(){

    double v[128][2];
    double x, y;
    
    int n = 0;
    while(scanf("%lf,%lf", &x, &y) != EOF){
        v[n][0] = x; v[n][1] = y;
        ++n;
    }
    
    double s = 0;
    for(int i=1;i<n-1;++i){
        double ts = fabs((v[i][0] - v[0][0])*(v[i+1][1] - v[0][1])
                         -(v[i+1][0] - v[0][0])*(v[i][1] - v[0][1])) / 2;
        s += ts;
    }
    
    printf("%.7f\n", s);
    
    return 0;
}