Let \( A, B \) and \( C \) be three events such that the probability that exactly one of \( A \) and \( B \) occurs is \( (1-k )\), the probability that exactly one of \( B \) and \( C \) occurs is \( 1-2k \), the probability that exactly one of \( C \) and \( A \) occurs is \( (1-k) \) and the probability of all \( A, B \) and \( C \) occur simultaneously is \( k^{2} \), where \( 0<k<1\).Then the probability that at least one of \(A\),\(B\) and \(C\) occur is :
