QBIC, 25 bytes
:[0,a,sgn(a)|A=A+!b$]?_lA
Explanation:
:[0,a Read 'a' from the cmd line, start a FOR loop from 0 to 'a'
,sgn(a)| with incrementer set to -1 for negative ranges and 1 for positive ones
A=A+!b$ Add a string cast of each iteration (var 'b') to A$
] NEXT
?_lA Print the length of A$
