{"problem":{"name":"D. Xor Sum","description":{"content":"You're given an array a with n elements.  Compute the xor sum of the elements that appear an odd number of times in the array a. The first line contains number n (1 ≤ n ≤ 3000000). The second line o","description_type":"Markdown"},"platform":"Codeforces","limit":{"time_limit":1000,"memory_limit":4096},"difficulty":"None","is_remote":true,"is_sync":true,"sync_url":null,"sign":"CF10074D"},"statements":[{"statement_type":"Markdown","content":"You're given an array a with n elements. \n\nCompute the xor sum of the elements that appear an odd number of times in the array a.\n\nThe first line contains number n (1 ≤ n ≤ 3000000). The second line of the input contains n numbers, representing the array a. All elements of a are between 0 and 109\n\nThe only line of the output contains the answer of the problem.\n\n## Input\n\nThe first line contains number n (1 ≤ n ≤ 3000000). The second line of the input contains n numbers, representing the array a. All elements of a are between 0 and 109\n\n## Output\n\nThe only line of the output contains the answer of the problem.\n\n[samples]","is_translate":false,"language":"English"},{"statement_type":"Markdown","content":"**Definitions**  \nLet $ n \\in \\mathbb{Z} $ be the length of the array.  \nLet $ A = (a_1, a_2, \\dots, a_n) $ be a sequence of integers, where $ a_i \\in \\{0, 1, \\dots, 10^9\\} $.\n\nLet $ f(x) $ denote the frequency of element $ x $ in $ A $.\n\n**Constraints**  \n1. $ 1 \\leq n \\leq 3 \\times 10^6 $  \n2. $ 0 \\leq a_i \\leq 10^9 $ for all $ i \\in \\{1, \\dots, n\\} $\n\n**Objective**  \nCompute the XOR sum of all elements $ x $ such that $ f(x) $ is odd:  \n$$\n\\bigoplus_{\\substack{x \\in A \\\\ f(x) \\text{ odd}}} x\n$$","is_translate":false,"language":"Formal"}],"meta":{"iden":"CF10074D","tags":[],"sample_group":[],"created_at":"2026-03-03 11:00:39"}}