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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<stdlib.h>

int cmp_1(const void *a,const void *b)
{
  return*(int*)a-*(int*)b;
}

int cmp_2(const void *a,const void *b)
{
  return*(int*)b-*(int*)a;
}

int main()
{
  int n;
  
  scanf("%d",&n);
  
  int a[n],b[n];
  int i;
  int ans;
  
  for(i=0;i<n;i++)
  {
    scanf("%d%d",&a[i],&b[i]);
  }
  
  qsort(a,n,sizeof(int),cmp_1);
  qsort(b,n,sizeof(int),cmp_2);
  
  ans=a[0]-1;
  for(i=1;i<n;i++)
  {
    ans+=a[i]-a[i-1]-1;
  }  
  ans+=b[n-1];

  printf("%d\n",ans+n);
  
  return 0;
}