program time;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  n: integer;
  function step (n: integer): int64;
    var
      i: integer;
      a: array [1..36] of int64;
    begin
      a[1] := 1;
      a[2] := 2;
      a[3] := 4;
      for i := 4 to n do begin
        a[i] := a[i-1] + a[i-2] + a[i-3];
      end;
      result := a[n];
    end;
begin
  readln (n);
  writeln (step(n));
  readln;
end.