Iterative Fibonacci Calculation

This problem requires you to implement an iterative approach to compute the nth Fibonacci number. The Fibonacci sequence is defined as follows:

\(F(0) = 0, \quad F(1) = 1\)

For \(n \ge 2\), the recurrence relation is given by:

\(F(n) = F(n-1) + F(n-2)\)

Your task is to calculate \(F(n)\) using a loop-based method which guarantees a time complexity of \(O(n)\) and a space complexity of \(O(1)\).

inputFormat

The input consists of a single integer \(n\) given via standard input (stdin). You can assume that \(0 \le n \le 90\) to avoid integer overflow issues.

outputFormat

Output the nth Fibonacci number to standard output (stdout).

## sample

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