Here is a version of the code converted back to C:

```c
#include <stdio.h>

// Function to calculate the nth Fibonacci number
int fibonacci(int n) {
    // Allocate space on the stack
    // Save the return address
    // Save the base case value
    // Save the previous value

    // Handle base cases
    if (n <= 0) {
        // Base case: fib(0) = 0
        return 0;
    } else if (n == 1) {
        // Initialize base cases
        // Handle second base case
        // Return the current value
        return 1;
    } else {
        // Recursive case
        // Save the previous value
        // Add previous value to current value
        return fibonacci(n-1) + fibonacci(n-2);
    }
}

int main() {
    int number;
    printf("Enter a number: ");
    scanf("%d", &number);
    printf("Fibonacci of %d = %d\n", number, fibonacci(number));

    // Restore saved registers
    // Deallocate stack space
    // Return to the calling function
    return 0;
}

```
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