Minimum number of bills

Given a natural number $N$ (8 \leq N \leq 1000000), which represents any integer sum of money not exceeding $1000000$. It is known that any integer sum of money greater than or equal to $7$ units can be given only using bills with denominations of $2$ and $5$ units. Determine the minimal number of bills of $2$ and $5$ units needed to make up the sum of $N$ units.