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<iomanip>
#include<cstdio>
#include<iostream>
#include<vector>
#include<cmath>
using namespace std;
typedef long double ll;
typedef pair<ll,ll> pll;
vector<pll> list;
pll operator-(pll a,pll b){
return pll(a.first-b.first,a.second-b.second);
}
ll dist(pll a){
return sqrt(a.first*a.first + a.second*a.second);
}
ll cal(pll a,pll b,pll c){
ll ab = dist(a-b);
ll bc = dist(b-c);
ll ca = dist(c-a);
ll z = (ab+bc+ca)/2;
return sqrt(z*(z-ab)*(z-bc)*(z-ca));
}
ll solve(){
ll ans=0;
for(int i=2;i<list.size();i++){
ans+=cal(list[0],list[i-1],list[i]);
}
return ans;
}
int main(){
char c;
ll x,y;
while(cin>>x>>c>>y){
list.push_back(pll(x,y));
}
cout<<solve()<<endl;
}