diff --git a/atcoder/fenwicktree.py b/atcoder/fenwicktree.py
new file mode 100644
index 0000000..c5250a9
--- /dev/null
+++ b/atcoder/fenwicktree.py
@@ -0,0 +1,53 @@
+import typing
+
+
+class FenwickTree:
+    '''Reference: https://en.wikipedia.org/wiki/Fenwick_tree'''
+
+    def __init__(self, n: int = 0) -> None:
+        self._n = n
+        self.data = [0] * n
+
+    def add(self, p: int, x: typing.Any) -> None:
+        assert 0 <= p < self._n
+
+        p += 1
+        while p <= self._n:
+            self.data[p - 1] += x
+            p += p & -p
+
+    def sum(self, left: int, right: int) -> typing.Any:
+        assert 0 <= left <= right <= self._n
+
+        return self._sum(right) - self._sum(left)
+
+    def _sum(self, r: int) -> typing.Any:
+        s = 0
+        while r > 0:
+            s += self.data[r - 1]
+            r -= r & -r
+
+        return s
+
+
+# https://atcoder.jp/contests/practice2/tasks/practice2_b
+def main() -> None:
+    import sys
+
+    n, q = map(int, sys.stdin.readline().split())
+    fenwick_tree = FenwickTree(n)
+
+    a = map(int, sys.stdin.readline().split())
+    for i, ai in enumerate(a):
+        fenwick_tree.add(i, ai)
+
+    for _ in range(q):
+        t, x, y = map(int, sys.stdin.readline().split())
+        if t == 0:
+            fenwick_tree.add(x, y)
+        if t == 1:
+            print(fenwick_tree.sum(x, y))
+
+
+if __name__ == '__main__':
+    main()