A customer has to go through four steps to complete a service: S$1,$ S$2,$ S$3,$ and S$4$ in this sequence. One server is assigned to work at each of the first, second, and last step. $2$ servers work at the third step to provide exactly the same service simultaneously to multiple customers.

The values below indicate the minutes each step takes.

Step S$1$ S$2$ S$3$ S$4$

Time $($min$)35122$

The capacity of this process is $\_\_\_\_\_$ customers per hour. Round to the nearest whole number if necessary.