OCC '19 G2 - A Guessing Game
View as PDFAlex is playing a game with William. Alex gets two sequences: sequence  and sequence 
, each of which has 
 numbers. Alex will show William the sequence 
 but not the sequence 
. The objective of this game is to figure out each number in sequence 
.
During the game, William can ask Alex questions as many times as he wants. For each question, William will pick up an interval  (
) and ask Alex the sum of 
 for 
. Alex will answer William's question, but will charge William for 
 dollars. William wants to use the minimal cost to figure out the sequence 
.
Since William is bored, he decides to play this game for  rounds. Before each round, Alex will re-generate the sequence 
. However, Alex is too lazy to re-generate the cost sequence 
. So, Alex will only change one number from the previous sequence 
. Given the number which Alex will change and the new value, can you help William to find out the minimum cost for figuring out the sequence 
 in each round of the game?
Constraints
For all subtasks:
.
| Subtask | Points | Additional constraints | 
|---|---|---|
| No additional constraints. | 
Input Specification
The first line contains two integers,  and 
, the number of elements in each sequence and the number of rounds William will play.
The second line contains  integers, the initial sequence 
.
 lines of input follow. The 
 line contains two integers, 
 and 
, which means Alex will pick up the 
 element from the previous sequence 
 and replace it with the new value 
 before round 
.
Output Specification
Print  lines. The 
 line contains one integer, the minimum cost for William to figure out the sequence 
 in game 
.
Sample Input
5 3
1 2 3 4 5
1 2
3 4
5 6
Sample Output
5
6
10
Explanation for Sample Output
The initial sequence  is 
.
Before round , Alex will change 
 to be 
, i.e. the new sequence 
 is 
.
In round , William can ask questions for 
, 
, 
, 
 and 
 with the total cost of 
.
Before round , Alex will change 
 to be 
, i.e. the new sequence 
 is 
.
In round , William can ask questions for 
, 
, 
, 
 and 
 with the total cost of 
.
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