Instead of $\binom{N}{c}$, $\binom{N}{N_1}$ should be appropriate since $c$ is not defined in this section. <img width="896" height="477" alt="Image" src="https://github.com/user-attachments/assets/aec96505-8de0-4f58-8e53-6d4aecd7ec8a" />
Instead of$\binom{N}{c}$ , $\binom{N}{N_1}$ should be appropriate since $c$ is not defined in this section.