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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Arrays;
import java.util.Scanner;

class Person implements Comparable<Person>{
	int A, B;
	public Person(int a, int b) {
		A = a; B = b;
	}
	public int compareTo(Person p) {
		return A - p.A;
	}
}

class Main{
	public static void main(String args[]){
		Scanner sc=new Scanner(System.in);
		int N = sc.nextInt();
		Person[] ps = new Person[N];
		for(int i = 0; i < N; i++) {
			ps[i] = new Person(sc.nextInt(), sc.nextInt());
		}
		Arrays.sort(ps);
		int rank = 0;
		long cnt = N;
		for(int i = 0; i < N; i++) {
			if(rank + 1 <= ps[i].A) {
				// 前の人との間に誰か居る
				cnt += (long)(ps[i].A - rank - 1);
				rank = ps[i].A;
			}
			if(i == N - 1) {
				// 最後の人
				cnt += (long)ps[i].B;
			}
		}
		System.out.println(cnt);
	}
}