I tried to find tasks that can be solved without reading all of input data. I found this 2:
Maybe someone know more tasks on codeforces that don`t require reading all of input?
Edit. My 2 + added in comments tasks:
1028B - Unnatural Conditions -|- 1004B - Sonya and Exhibition -|- 869A - The Artful Expedient -|- 630A - Again Twenty Five! -|- 100812K - Might and Magic -|- 100625F - Flying Safely -|- 765A - Neverending competitions -|- 296A - Yaroslav and Permutations -|- 659D - Bicycle Race