Doesn't it depend on N?
If N!/(N-R)! = N*(N-1)*(N-2)*...*(N-R+1)*(N-R)!/((N-R)!
= N*(N-1)*(N-2).......*(N-R+1) ---- (1)
(1) can be less than 1000 in several cases sependong on N.
For N<32, R=1
For N>32, R=0 is the only solution.
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