Problem:
Score : 300 points

Problem Statement

Given are an integer X and an integer sequence of length N: p_1, \ldots, p_N.

Among the integers not contained in the sequence p_1, \ldots, p_N (not necessarily positive), find the integer nearest to X, that is, find the integer whose absolute difference with X is the minimum. If there are multiple such integers, report the smallest such integer.

Constraints

1 \leq X \leq 100

0 \leq N \leq 100

1 \leq p_i \leq 100

p_1, \ldots, p_N are all distinct.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X N
p_1 ... p_N

Output

Print the answer.

Sample Input 1

6 5
4 7 10 6 5

Sample Output 1

8

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the one nearest to 6 is 8.

Sample Input 2

10 5
4 7 10 6 5

Sample Output 2

9

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the ones nearest to 10 are 9 and 11. We should print the smaller one, 9.

Sample Input 3

100 0

Sample Output 3

100

When N = 0, the second line in the input will be empty. Also, as seen here, X itself can be the answer.

Solution in C (GCC 9.2.1) (judge verdict: Accepted)

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

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

int main(void) {
  int x, n;
  scanf("%d %d", &x, &n);
  int num[n];
  if (!n) {
    printf("%d\n", x);
  } else {
    for (int i = 0; i < n; i++) {
      scanf(" %d", &num[i]);
    }

    qsort(num, n, sizeof(int), cmp_int);

    for (int i = 0; i < n; i++) {
      if (x < num[i]) {
        printf("%d\n", x);
        break;
      } else if (x > num[i]) {
        continue;
      } else if (x == num[i]) {
        int low = x - 1;
        int high = x + 1;

        for (int j = i - 1; j > -1; j--) {
          if (low != num[j]) {
            break;
          }
          low--;
        }

        for (int j = i + 1; j < n; j++) {
          if (high != num[j]) {
            break;
          }
          high++;
        }

        if ((x - low) > (high - x)) {
          printf("%d\n", high);
          break;
        } else {
          printf("%d\n", low);
          break;
        }
      }
    }
  }

  return 0;
}