To solve this problem, we need to determine the number of valid pairs of non-empty substrings (A, B) such that their concatenation (A+B) equals the given string S.

Approach

The key insight here is that for the concatenation of two substrings A and B to form the entire string S, A must be a prefix of S and B must be the corresponding suffix of S (starting immediately after A). This is because the concatenation of A and B must exactly match S.

For a string of length N:

• We can split S into A and B at any position k (where 1 ≤ k ≤ N-1).
• Each split k gives exactly one valid pair (A, B) where A is the prefix of length k and B is the suffix of length N-k.
• Both A and B are non-empty and are valid substrings of S.

Thus, the number of valid pairs is simply N-1 (if N ≥ 2; if N=1, there are no valid pairs as we can't split into two non-empty parts).

Solution Code

s = input().strip()
n = len(s)
print(n-1 if n >=2 else 0)

Explanation

• Input Handling: We read the input string and compute its length.
• Result Calculation: If the length of the string is at least 2, the number of valid pairs is the length minus one (since there are N-1 possible split points). If the length is 1, the result is zero as no valid split exists.

This approach efficiently computes the result in O(1) time (after reading the input) since it only involves checking the length of the string and performing a simple arithmetic operation. The time complexity is O(N) for reading the input string, which is optimal for this problem.

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