# Floor function

Algebra Level 5

$x - f(x) = 19 \left \lfloor \frac x{19} \right \rfloor - 90 \left \lfloor \frac {f(x)}{90} \right \rfloor \\ 1900 < f(1990) < 2000$

Suppose $$f: N \rightarrow N$$ satisfies the conditions above, find the sum of all possible values of $$f(1990)$$.

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