AT_abc430_c [ABC430C] Truck Driver

> In AtCoder Country, there is a rule that "a truck driver must take a break of at least $ B $ minutes when driving for $ A $ minutes or more." You are given a string $ S $ of length $ N $ consisting of `a` and `b`, and positive integers $ A $ and $ B $ . Find the number of integer pairs $ (l,r) $ that satisfy all of the following conditions. - $ 1\leq l \leq r \leq N $ - The number of `a` in the substring from the $ l $ -th character through the $ r $ -th character of $ S $ is greater than or equal to $ A $ . - The number of `b` in the substring from the $ l $ -th character through the $ r $ -th character of $ S $ is less than $ B $ .

The input is given from Standard Input in the following format: > $ N $ $ A $ $ B $ $ S $

Print the answer.

### Sample Explanation 1 The pairs $ (l,r) $ that satisfy the conditions are $ (4,8),(4,9),(5,9) $ , which is three pairs. ### Sample Explanation 2 There are no pairs $ (l,r) $ that satisfy the conditions. ### Constraints - $ 1\leq N \leq 3\times 10^5 $ - $ 1 \leq A,B \leq N $ - $ S $ is a string of length $ N $ consisting of `a` and `b`. - All input numbers are integers.