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source/DS/Fenwick.cpp

@@ -0,0 +1,9 @@
+ll tree[N];
+void update(int i,ll x) {
+    while(i < N) tree[i] += x, i += i&-i;
+}
+int query(int i) {
+    ll s = 0;
+    while(i) s += tree[i], i -= i&-i;
+    return s;
+}