from unittest import TestCase

class Fenwick:
    def __init__(self, n):
        self.n = n
        self.tree = [0] * (n + 1)

    def add(self, i, delta):
        while i <= self.n:
            self.tree[i] += delta
            i += i & -i

    def sum(self, i):
        res = 0
        while i > 0:
            res += self.tree[i]
            i -= i & -i
        return res

    def sum_range(self, i, j):
        return self.sum(j) - self.sum(i - 1)

class TestFenwick(TestCase):
    def test_fenwick(self):
        tree = Fenwick(10)
        tree.add(1, 1)
        tree.add(2, 2)
        tree.add(3, 3)
        self.assertEqual(tree.sum(1), 1)
        self.assertEqual(tree.sum(2), 3)
        self.assertEqual(tree.sum(3), 6)
        self.assertEqual(tree.sum(2, 3), 5)
        tree.add(1, 100)
        self.assertEqual(tree.sum(3), 106)