poj2954

水题，先用叉积求三角形面积
然后求三边上的点（由公约数上点）a
然后用pick定理S=a+b/2-1
就可以求出内部的点数了

var x,y,xx,yy,a1,a2,a3,x1,x2,x3,y1,y2,y3:longint;
    s,ans:double;

function gcd(a,b:longint):longint;
  begin
    if b=0 then exit(a)
    else exit(gcd(b,a mod b));
  end;

begin
  readln(x1,y1,x2,y2,x3,y3);
  while not((x1=0) and (x2=0) and (x3=0) and (y1=0) and (y2=0) and (y3=0)) do
  begin
    x:=x2-x1;
    y:=y2-y1;
    xx:=x3-x1;
    yy:=y3-y1;
    s:=abs(x*yy-y*xx)/2;
    a1:=gcd(abs(x1-x2),abs(y1-y2));
    a2:=gcd(abs(x1-x3),abs(y1-y3));
    a3:=gcd(abs(x2-x3),abs(y2-y3));
    ans:=s+1-(a1+a2+a3)/2;
    writeln(ans:0:0);
    readln(x1,y1,x2,y2,x3,y3);
  end;
end.