#include<stdio.h> #include<math.h>

int main() { int a,b,c,d,e,f; while(scanf("%d %d %d %d %d %d",&a,&b,&c,&d,&e,&f)!=EOF) { if(a0&&b0&&c0&&d0&&e0&&f0) break; double s; s=(ad+cf+eb-af-cb-ed)*0.5; if(s<0) s=-s; printf("%.1lf\n",s); } }