IMSO 2018 — Math Division — Short Answer Question 15

Let $I$, $M$, $S$ and $O$ represent different digits and the sum of $IMSO$, $ISMO$, $OMSI$, $OSMI$, $MISO$, $MOSI$, $SIMO$ and $SOMI$ is equal to 60012. What is the value of $I+M+S+O$?