Mooo Moo

Farmer John forgot how many cows he owns. He placed microphones in $N$ fields along a road to estimate cow counts from mooing volume.

Breed $i$ moos at volume $V(i)$. Wind blows left to right: if a field's total volume is $X$, the next field gains $max(0, X-1)$ from carryover.

Given recorded total volumes, find the minimum possible number of cows, or $-1$ if impossible.

Line 1: $N$, $B$.

Next $B$ lines: $V(i)$.

Next $N$ lines: recorded volume in each field.

Minimum number of cows, or $-1$.