Program Fibo;
Var
	IsFibo, FirstTime:Boolean;
	A,B,Num:Integer; { A - המספר הקודם הראשון , B - המספר הקודם השני }
Begin
	IsFibo:=True;
	FirstTime:=True;
	Write('Input the first number: ');
	Readln(A);
	Write('Input the second number: ');
	Readln(B);
	Repeat
		Write('Input a number ( type -1 for ESC ):');
		Readln(Num);
		If Not (A+B  = Num) And ( (Not Num=-1) Or (Num=-1 And FirstTime)) Then
			IsFibo:=False;
		A:=B;
		B:=Num;
		FirstTime:=False;
	Until Num = -1;
	
	Writeln('Is fibo?:',IsFibo);
	Readln;
End.