A person eats $X ( > 1)$ cookies in $N$ days in the following way:
- He eats $1$ plus $1/7$ of the remaining cookies on the $1^{st}$ day
- He eats $2$ plus $1/7$ of the remaining cookies on the $2^{nd}$ day
- $\cdots$
- Finally, he eats the last $N$ cookies on the $N^{th}$ day
What is the smallest possible value of $X$?