riff 1
|---------------------|
|---------------------|
|---------------------|
| 0--4--0--5--0--4--0-|

riff 2	
|-----------------------------------|
|-----------------------------------|
|-----------------------------------|
|0--4--0--5--0--4--0-5-0-4-0-5-0-4-0|

sequence of riffs : 1 1 2 1 1 2 1 1 1...
in the finish : 1 1 2