6. Suppose \( X \) and \( Y \) are random variables with \( E(Y|X = x) = -X + 3 \) and \( E(X|Y = y) = -\frac{1}{4} Y + 5 \). Then, the correlation coefficient between \( X \) and \( Y \), \( \operatorname{Corr}(X,Y) \), equals      (6)     .