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Given a length n, count the number of strings of length n that can be made using ‘a’, ‘b’ and ‘c’ with at-most one ‘b’ and two ‘c’s allowed.

**Example 1:**

Input:n = 1Output:3Explanation:Possible strings are: "a", "b" and "c"

**Example 2:**

**Input:** n = 3
**Output:** 19
**Explanation:** Number of strings with 3
occurrances of a: 1
2-a and 1-b: 3
2-a and 1-c: 3
1-a, 1-b and 1-c: 6
1-a and 2-c: 3
1-b and 2-c: 3
So, total number of strings of length 3
is 1 + 3 + 3 + 6 + 3 + 3 = 19

**Your Task: **

You don't need to read input or print anything. Your task is to complete the function **countStr****()** which takes the **n**** **as inputs and returns the answer.

**Expected Time Complexity:** O(1)

**Expected Auxiliary Space:** O(1)

**Constraints:**

1 ≤ n ≤ 10^{5}

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Count of strings that can be formed using a, b and c under given constraints

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