Mr. Hacker's Department of Administrative Affairs (DAA) has infinite civil servants. Every integer is used as an id number by exactly one civil servant. Mr. Hacker is keen on reducing overmanning in civil service, so he will only keep people with consecutive id numbers in $[l,r]$ and dismiss others.
However, permanent secretary Sir Humphrey's id number is $x$ and he cannot be kicked out so there must be $l \leq x \leq r$. Mr. Hacker wants to be Prime Minister so he demands that the sum of people's id number $\sum_{i=l}^r i$ must be a prime number.
You, Bernard, need to make the reduction plan which meets the demands of both bosses. Otherwise, Mr. Hacker or Sir Humphrey will fire you.
Mr. Hacker would be happy to keep as few people as possible. Please calculate the minimum number of people left to meet their requirements.
A prime number $p$ is an integer greater than $1$ that has no positive integer divisors other than $1$ and $p$.