var f:array[0..1000]of longint;
       i,n:longint;
procedure setio;
begin
	assign(input,'domino.in');
	assign(output,'domino.out');
	reset(input);
	rewrite(output);
end;
procedure print;
begin
	close(input);
	close(output);
end;
begin
        setio;
        readln(n);
        f[0]:=1; f[1]:=1; f[2]:=2;
        for i:=3 to n do
          f[i]:=f[i-1]+f[i-2]+f[i-3];
        writeln(f[n]);
        print;
end.