n =: 678910
L =: 123
k =: #":L

NB. If it doesn't work, increse the limit by hand (increase 1.1)
NB. This limit is set based on Benford's law
limit =: <. 1.1 * n * %10^.1+%L

problem686 =: (n-1) { I. L=<.10^_1+k+1|(10^.2)*i.limit