#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <vector>
typedef long long ll;
typedef unsigned long long ull;
typedef long double LD;
using namespace std;
const int INF = 2147483647;
const int INF2 = 0x3f3f3f3f;
const ll INF64 = 3e18;
const double INFD = 1e30;
const double EPS = 1e-9;
const double PI = acos(-1);
const int MOD = 1000000007;
template <typename T>
inline T read() {
    T X = 0, w = 0;
    char ch = 0;
    while (!isdigit(ch)) {
        w |= ch == '-';
        ch = getchar();
    }
    while (isdigit(ch)) X = (X << 3) + (X << 1) + (ch ^ 48), ch = getchar();
    return w ? -X : X;
}
const int MAXN = 5005;
int n, m, k;
int dr[4] = {1, 0, -1, 0};
int dc[4] = {0, 1, 0, -1};
int dr2[8] = {1, 1, 1, -1, -1, -1, 0, 0};
int dc2[8] = {1, 0, -1, 1, 0, -1, 1, -1};
int CASE = 1;
int dcmp(double x) {
    if (fabs(x) < EPS) return 0;
    return x > 0 ? 1 : -1;
}

struct Vector2 {
    double x, y;
    Vector2() {}
    Vector2(double x, double y) : x(x), y(y) {}
    Vector2(double rad) : x(cos(rad)), y(sin(rad)) {}
    friend istream& operator>>(istream& input, Vector2& v) {
        input >> v.x >> v.y;
        return input;
    }
    friend ostream& operator<<(ostream& output, const Vector2& v) {
        output << '(' << v.x << ',' << v.y << ')';
        return output;
    }
    static double dot(const Vector2& a, const Vector2& b) {
        return a.x * b.x + a.y * b.y;
    }
    static double angle(const Vector2& a, const Vector2& b) {
        return acos(dot(a, b) / a.length() / b.length());
    }
    static double cross(const Vector2& a, const Vector2& b) {
        return a.x * b.y - a.y * b.x;
    }
    static double area2(const Vector2& a, const Vector2& b, const Vector2& c) {
        return cross(b - a, c - a);
    }

    double length() const { return sqrt(x * x + y * y); }
    double lengthSq() const { return x * x + y * y; }
    double getRad() const { return atan2(y, x); }
    Vector2 rotate(double rad) const {
        return Vector2(x * cos(rad) - y * sin(rad),
                       x * sin(rad) + y * cos(rad));
    }
    Vector2 unit() const {
        double l = this->length();
        return Vector2(x / l, y / l);
    }
    Vector2 normal() const {
        double l = this->length();
        return Vector2(-y / l, x / l);
    }

    bool operator<(const Vector2& other) const {
        return x < other.x || (x == other.x && y < other.y);
    }
    bool operator==(const Vector2& other) const {
        return !dcmp(x - other.x) && !dcmp(y - other.y);
    }

    Vector2& operator+=(const Vector2& vec) {
        this->x += vec.x, this->y += vec.y;
        return *this;
    }
    Vector2 operator+(const Vector2& vec) const {
        return Vector2(this->x + vec.x, this->y + vec.y);
    }
    Vector2& operator-=(const Vector2& vec) {
        this->x -= vec.x, this->y -= vec.y;
        return *this;
    }
    Vector2 operator-(const Vector2& vec) const {
        return Vector2(this->x - vec.x, this->y - vec.y);
    }
    Vector2& operator*=(double v) {
        this->x *= v, this->y *= v;
        return *this;
    }
    Vector2& operator*=(const Vector2& v) {
        this->x *= v.x, this->y *= v.y;
        return *this;
    }
    Vector2 operator*(double v) const {
        return Vector2(this->x * v, this->y * v);
    }
    Vector2 operator*(const Vector2& vec) const {
        return Vector2(this->x * vec.x, this->y * vec.y);
    }
    Vector2& operator/=(double v) {
        this->x /= v, this->y /= v;
        return *this;
    }
    Vector2& operator/=(const Vector2& vec) {
        this->x /= vec.x, this->y /= vec.y;
        return *this;
    }
    Vector2 operator/(double v) const {
        return Vector2(this->x / v, this->y / v);
    }
    Vector2 operator/(const Vector2& vec) const {
        return Vector2(this->x / vec.x, this->y / vec.y);
    }
};

struct Line {
    Vector2 p, dir;
    Line() {}
    Line(const Vector2& p, const Vector2& dir) : p(p), dir(dir) {}
    static Vector2 lineIntersection(const Line& l1, const Line& l2) {
        double t = Vector2::cross(l2.dir, l1.p - l2.p) /
                   Vector2::cross(l1.dir, l2.dir);
        return l1.p + l1.dir * t;
    }
    static double distanceToLine(const Vector2& p, const Line& line) {
        return fabs(Vector2::cross(line.dir, p - line.p)) / line.dir.length();
    }

    static Vector2 lineProjection(const Vector2& p, const Line& l) {
        return l.p + l.dir * Vector2::dot(l.dir, p - l.p) /
                         Vector2::dot(l.dir, l.dir);
    }
};

struct Segment {
    Vector2 p1, p2;
    Segment() {}
    Segment(const Vector2& p1, const Vector2& p2) : p1(p1), p2(p2) {}
    static double distanceToSegment(const Vector2& p, const Segment& seg) {
        if (seg.p1 == seg.p2) return (p - seg.p1).length();
        Vector2 ab = seg.p2 - seg.p1, ap = p - seg.p1, bp = p - seg.p2;
        if (dcmp(Vector2::dot(ab, ap)) < 0)
            return ap.length();
        else if (dcmp(Vector2::dot(ab, bp)) > 0)
            return bp.length();
        else
            return fabs(Vector2::cross(ab, ap) / ab.length());
    }
    static bool properIntersection(const Segment& s1, const Segment& s2) {
        double c1 = Vector2::cross(s1.p2 - s1.p1, s2.p1 - s1.p1),
               c2 = Vector2::cross(s1.p2 - s1.p1, s2.p2 - s1.p1),
               c3 = Vector2::cross(s2.p2 - s2.p1, s1.p1 - s2.p1),
               c4 = Vector2::cross(s2.p2 - s2.p1, s1.p2 - s2.p1);
        return dcmp(c1) * dcmp(c2) < 0 && dcmp(c3) * dcmp(c4) < 0;
    }
    static bool onSegment(const Vector2& p, const Segment& s) {
        return !dcmp(Vector2::cross(s.p1 - p, s.p2 - p)) &&
               dcmp(Vector2::dot(s.p1 - p, s.p2 - p)) < 0;
    }
};

int main() {
#ifdef LOCALLL
    freopen("in", "r", stdin);
    freopen("out", "w", stdout);
#endif
    scanf("%d%d", &m, &n);
    set<int> a;
    for (int i = 0; i < n; i++) {
        a.insert(read<int>());
    }
    int ans = -1;
    for (int i = 0; i < 200; i++) {
        if (!a.count(m - i)) {
            ans = m - i;
            break;
        }
    }
    for (int i = 0; i < 200; i++) {
        if (!a.count(m + i)) {
            if (abs(ans - m) > i) {
                ans = m + i;
            }
            break;
        }
    }
    printf("%d\n", ans);
    return 0;
}

Measured memory_bytes: 3800