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: Wrong Answer)

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

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

int binarySearch(int arr[], int l, int r, int x) 
{ 
    while (l <= r) { 
        int m = l + (r - l) / 2; 
        if (arr[m] == x) 
            return m; 
        else if (arr[m] < x) 
            l = m + 1; 
        else
            r = m - 1; 
    } 
    return -1; 
}

int main(void) {
  int X, N;
  scanf("%d %d", &X, &N);
  int p[N], i;
  for(i = 0; i < N; ++i)
    scanf("%d", &p[i]);
  int b, a, min = 100, ans = 0, absolute = 0;
  qsort(p, N, sizeof(int), comfun);
  for(i = p[0]; i <= p[N - 1]; ++i){
    b = binarySearch(p, 0, N - 1, i);
    if(b == -1){
      a = X - i;
      absolute = abs(a);
      if(absolute < min){
        min = absolute;
        ans = i;
      }
    }
    else if(b != -1) 
      continue;
  }
  printf("%d\n", ans);
  return 0;
}