The index of a Fibonacci number

Explanation of the Code

1. Reading Input:
   a = int(input())

   • The input() function reads a line of text from the user.
   • The int() function converts this input to an integer and stores it in the variable a.
2. Handling Base Cases:
   if a == 0:
    print(0)
 elif a == 1:
    print(1)

   • If $a$ is 0, print 0.
   • If $a$ is 1, print 1.
3. Calculating Fibonacci Number and Its Index:
   else:
fib_0 = 0
fib_1 = 1
index = 1
    while fib_1 < a:
fib_n = fib_0 + fib_1
fib_0 = fib_1
fib_1 = fib_n
index += 1
if fib_1 == a:
print(index)
else:
print(-1)

   • Initialize fib_0 to 0 and fib_1 to 1.
   • Initialize index to 1.
   • Use a while loop to iterate and generate Fibonacci numbers until fib_1 is greater than or equal to $a$.
   • In each iteration, calculate the next Fibonacci number (fib_n) as the sum of the previous two Fibonacci numbers.
   • Update fib_0 to the value of fib_1 and fib_1 to the value of fib_n.
   • Increment index by 1.
   • After the loop, if fib_1 equals $a$, print the value of index. Otherwise, print -1.