1) http://codeforces.com/problemset/problem/520/B
2) https://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=288
3) https://www.spoj.com/problems/PT07Y/
4) https://codeforces.com/problemset/problem/115/A
5) https://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=216
6) https://codeforces.com/contest/522/problem/A
7) https://www.spoj.com/problems/PT07Z/
8) https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=3104
9) https://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=1393