import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int X = sc.nextInt();
        int N = sc.nextInt();
        int[] p = new int[N];
        boolean[] q = new boolean[102];
        for(int i=0; i<N; i++){
            p[i]=sc.nextInt();
            q[p[i]] = true;
        }

        int res=X;
        for(int i=0; i<X+1; i++){
            if(!q[X-i]){
                res=X-i;
                System.out.println(res);
                return;
            }
            if(!q[X+i]){
                res=X+i;
                System.out.println(res);
                return;
            }
        }
        if(X>50){
            res=101;
        }else{
            res=-1;
        }
        System.out.println(res);
        
    
        }
    }
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz