def compute_num(x, y): sum_num = 0 for i in range(x, y+1): if i in [2, 3]: sum_num += i continue for j in range(3, i//2 + 1): if i % j == 0: break if j == i // 2: sum_num += i return sum_num

a, b = map(int, input().split()) print(compute_num(a, b))