Preparation details
==================
### Div.2 A:-
problem author : me

solution author : me

testers : [user:mahmoudbadawy,2017-01-31] and [user:zoooma13,2017-01-31]

### Div.2 B:-
problem author : me

solution authors : me and [user:mahmoudbadawy,2017-01-31]

tester : [user:zoooma13,2017-01-31]

### Div.1 A:-
problem authors : me and [user:mahmoudbadawy,2017-01-31]

solution authors : me and [user:mahmoudbadawy,2017-01-31]

tester : [user:zoooma13,2017-01-31]

### Div.1 B:-
problem author : [user:mahmoudbadawy,2017-01-31]

solution author : [user:mahmoudbadawy,2017-01-31]

testers : me and [user:zoooma13,2017-01-31]

and I'd like to thank [user:moaz123,2017-01-31] for helping in the preparation.

### Div.1 C:-
problem author : [user:mahmoudbadawy,2017-01-31]

solution author : me

testers : [user:mahmoudbadawy,2017-01-31] and [user:zoooma13,2017-01-31]

and I'd like to thank [user:moaz123,2017-01-31] for helping in the preparation.

### Div.1 D:-
problem author : me

solution author : me

tester : [user:mahmoudbadawy,2017-01-31]

Hints
==================
### Div.2 A:-

<spoiler summary="hint #1">
After entering some name, Can you make nothing happen if it occurred before ?
</spoiler>

### Div.2 B:-
#### Hints for solution #1:-

<spoiler summary="hint #1">
Think of this palindrome testing code:-


~~~~~
For i from 0 to s.size()/2
    If s[i]!=s[s.size()-i-1]
    //s isn't palindrome
~~~~~


</spoiler>



#### Hints for solution #2:-

<spoiler summary="hint #1">
If some $l$ makes them happy, Is it possible that $l-1$ makes them sad ?
</spoiler>

### Div.1 A:-

#### making the algorithm fail:-

<spoiler summary="hint #1">
Is there some type of trees such that its vertex cover differs as $n$ differs but the wrong algorithm gets a constant answer ?
</spoiler>

#### making the algorithm pass:-

<spoiler summary="hint #1">
Is there some type of trees with constant vertex cover and constant answer while using the wrong algorithm ?
</spoiler>

### Div.1 B

<spoiler summary="hint #1">
The solution works with $k \le 10^{18}$.
</spoiler>

<spoiler summary="hint #2">
Which path will Mahmoud take if $k$ is greater than the Manhattan distance between him and the exit ?
</spoiler>

<spoiler summary="hint #3">
If you got hint #2, You want to solve the problem with $k \le 200$, If you still don't realize it read the next hint.
</spoiler>

<spoiler summary="hint #4">
Would Mahmoud ever want to visit the same cell with the same number of bombs with him twice ?
</spoiler>