program a1 var integer function fib integer integer begin if then fib

program a1;
var n : integer;
 function fib(n: integer): integer;
  begin
   if (n = 0) then fib := 1
   else if (n = 1) then fib := 2
   else if (n = 2) then fib := 3
              else fib := fib(n-1)+fib(n-2)+fib(n-3);
  end;
begin
 write('vvedite N:'); readln(n);
 writeln('Fib(N): ', fib(n));
 readln;
end.