lab1.2 delphi

Var
    a, b, n: Integer;
    IsCorrect: Boolean;

Begin
    a := 1;
    b := 1;
    Writeln('The program will calculate the n-th term of the Fibonacci series.');
    Write('Enter the Fibonacci series member number: ');
    Repeat
        Try
            IsCorrect := True;
            Read(n);
            If (n < 0) Or (n = 0) Then
            Begin
                IsCorrect := False;
                Write('A negative value or zero was entered. Enter a valid value: ');
            End;
        Except
            Begin
                Write('Symbols have been entered. Enter the number: ');
                IsCorrect := False;
            End;
         End;
    Until IsCorrect;

    For Var i := 2 To n - 1 Do
    Begin
        b := a + b;
        a := b - a;
    End;
    Write(b);
End.