One vertex of a rectangular parallelopiped is at the origin \( O \) and the lengths of its edges along \( x, y \) and \( z \) axes are \( 3, 4 \) and \( 5 \) units respectively. Let \( P \) be the vertex \( (3,4,5) \). Then the shortest distance between the diagonal \( OP \) and an edge parallel to \( z \)-axis, not passing through \( O \) or \( P \) is:
