Var
 x,y,t,z:real;
 v:byte;
Begin
 Writeln('First vector:');
 Write('x= ');
 Readln(x);
 Write('y= ');
 Readln(y);
 Writeln('Second vector:');
 Write('x= ');
 Readln(t);
 Write('y= ');
 Readln(z);
 Repeat
  Writeln('Choose the action:');
  Writeln('   1 - sum of vectors');
  Writeln('   2 - difference between vectors');
  Writeln('   3 - scalar product');
  Writeln('   4 - sum of lengths');
  Writeln('   5 - exit');
  Readln(v);
  If (v=0) or (v>5) then v:=5;
  Case v of
   1: begin
       writeln('x= ',(x+t):0:3);
       writeln('y= ',(y+z):0:3);
      end;
   2: begin
       writeln('x= ',(x-t):0:3);
       writeln('y= ',(y-z):0:3);
      end;
   3: writeln((x*t+y*z):0:3);
   4: writeln((Sqrt(x*x+y*y)+Sqrt(t*t+z*z)):0:3);
  end;
 Until v=5;
End.