Codeforcesda mana bu savollarni yechayapmiz:

800 https://codeforces.com/problemset/problem/1891/A
1300 https://codeforces.com/problemset/problem/1870/C
1700 https://codeforces.com/problemset/problem/1934/C
1900 https://codeforces.com/problemset/problem/1902/E