Integers up to 1000 built from fours and fives

How many integers from $1$ to $1000$ can be expressed as a sum of one or more terms, each equal to $4$ or $5$ (for example $21=4+4+4+4+5$)?

$994$. Since $\gcd(4,5)=1$, every integer from $4\cdot5-4-5+1=12$ upward is representable (Frobenius number $11$). Checking below $12$, the failures are $1,2,3,6,7,11$, so $1000-6=994$ work.