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The index of a Fibonacci number


Statement

The Fibonacci sequence is defined as follows: $$ \phi_0 = 0, \ \phi_1 = 1, \ \phi_n = \phi_{n-1} + \phi_{n-2} . $$ Given an integer \( a \), determine its index among the Fibonacci numbers, that is, print the number \( n \) such that \( \phi_n = a \). If \( a \) is not a Fibonacci number, print -1.
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In all the problems input the data using input() and print the result using print().

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