#include <bits/stdc++.h>
using namespace std;
int main(){
    double k0,k1,k2,k3,k4,k5,k6,k7,k8;
    cin>>k0>>k1>>k2>>k3>>k4>>k5;
    k6=k0*k3+k2*k5+k1*k4;
    k7=k1*k2+k3*k4+k5*k0;
    k8=abs((k6-k7)/2);
    cout<<k8;
    return 0;
}