Let Ln denote the length of the longest common subsequence of two
sequences of length n. We draw one of the sequences i.i.d., but the other is non-
random and periodic. We prove that VAR[Ln] = (n). For such setup, our result
rejects the Chvatal-Sanko conjecture (1975) that VAR[Ln] = o(n
2
3 ) and answers
to Waterman's question (1994), whether the linear bound on VAR[Ln] can be im-
proved.