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 OCaml (4.02.3) (judge verdict: Accepted)

let inf = 101010101010101010
let _ = Scanf.scanf "%d" @@ fun n ->
  let a = Array.init (n+1) (fun i ->
    if i = 0 then (0, inf) else Scanf.scanf " %d %d" (fun x y -> -x, y)) in
  Array.sort compare a;
  Array.fold_left (fun (s, (x',y')) (x,y) ->
    s + min (x-x') (y-y'), (x,y)) (snd a.(0), a.(0)) a
  |> fst |> Printf.printf "%d\n"