#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;
}