Problem:
Score : 200 points

Problem Statement

A group of people played a game. All players had distinct scores, which are positive integers.

Takahashi knows N facts on the players' scores. The i-th fact is as follows: the A_i-th highest score among the players is B_i.

Find the maximum possible number of players in the game.

Constraints

1 \leq N \leq 10^5

1 \leq A_i \leq 10^9(1\leq i\leq N)

0 \leq B_i \leq 10^9(1\leq i\leq N)

If i ≠ j, A_i ≠ A_j.

There exists a possible outcome of the game that are consistent with the facts.

All input values are integers.

Inputs

Input is given from Standard Input in the following format:

N
A_1 B_1
:
A_N B_N

Outputs

Print the maximum possible number of players in the game.

Sample Input 1

3
4 7
2 9
6 2

Sample Output 1

8

The maximum possible number of players is achieved when, for example, the players have the following scores: 12,9,8,7,5,2,1,0.

Sample Input 2

5
1 10
3 6
5 2
4 4
2 8

Sample Output 2

7

Sample Input 3

2
1 1000000000
1000000000 1

Sample Output 3

1000000001

Solution in Ruby (2.3.3) (judge verdict: Accepted)

lines = $stdin.read
array = lines.split("\n")

n = array[0].to_i

score_h = {}
1.upto(n) do |index|
  index,score = array[index].to_s.split(" ").map(&:to_i)
  score_h[index] = score
end

#puts "max value => #{score_h.keys.min} => #{score_h[score_h.keys.min]}"
#puts "min value => #{score_h.keys.max} => #{score_h[score_h.keys.max]}"

top      = score_h.keys.min - 1
interval = score_h.keys.max - score_h.keys.min + 1
bottom   = score_h[score_h.keys.max]

#puts "^ ... = #{score_h.keys.min - 1}"
#puts "| ... = #{interval}"
#puts "_ ... = #{score_h[score_h.keys.max]}"

puts top + interval + bottom