How do you find the bottleneck of a process when one type of job flows through the system?

For example, you start at process 1 from there on it branches into 2 separate processes and then comes back together to rejoin again at process 4.

If each station's capacity is given can you assume the bottleneck is the one with the lowest capacity? But this isn't a single-line process so you shouldn't. Therefore, how do you identify the bottleneck?