var line = System.Console.In.ReadLine().TrimToNull();
while ( !System.String.IsNullOrEmpty( line ) ) {
	foreach ( var word in ReadWord( line ) ) {
		var operator = FindWord( word );
		if ( null == operator ) {
			var wordNotFound = new System.InvalidOperationException( "word not found: " + word );
			wordNotFound.Data.Add( "word", word );
			throw wordNotFound;
		}
		stack = operator.Execute( stack );
	}
	line = System.Console.In.ReadLine().TrimToNull();
}