l, r, m = map(int, input().split())
ql, rl = divmod(l, m)
qr, rr = divmod(r, m)
if qr - ql > 1:
    print(m)
elif qr - ql == 1:
    print(min(m, rr + m - rl + 1))
else:
    print(rr - rl + 1)