How many different/unique 4-letter arrangements are there of the letters in the word MISSISSAUGA

Question

So far I've broken it off to:-

$M=1$

$I=2$

$S=4$

$A=2$

$U=1$

$G=1$

However, I don't really know what to do next. An answer (with steps please) would be greatly appreciated. This seems to be a really important question :)