Let \( ABCD \) be a quadrilateral. If \( E \) and \( F \) are the mid points of the diagonals \( AC \) and \( BD \) respectively and \( (\overrightarrow{AB}-\overrightarrow{BC})+(\overrightarrow{AD}-\overrightarrow{DC}) = k\,\overrightarrow{FE} \), then \( k \) is equal to:
