#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define sz(a) int(a.size())
template <typename A, typename B>
ostream& operator <<(ostream& out, const pair<A, B>& a) { out << "(" << a.first << "," << a.second << ")"; return out; }
template <typename T, size_t N> ostream& operator <<(ostream& out, const array<T, N>& a) { out << "["; bool first = true; for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]"; return out; }
template <typename T> ostream& operator <<(ostream& out, const vector<T>& a) { out << "["; bool first = true; for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]"; return out; }
template <typename T, class Cmp> ostream& operator <<(ostream& out, const set<T, Cmp>& a) { out << "{"; bool first = true; for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "}"; return out; }
template <typename U, typename T, class Cmp> ostream& operator <<(ostream& out, const map<U, T, Cmp>& a) { out << "{"; bool first = true; for (auto& p : a) { out << (first ? "" : ", "); out << p.first << ":" << p.second; first = 0;} out << "}"; return out; }
template <typename Arg1> void __f(const char* name, Arg1&& arg1){ cerr << name << ": " << arg1 << endl; }
template <typename Arg1, typename... Args> void __f(const char* names, Arg1&& arg1, Args&&... args){ const char* comma = strchr(names + 1, ','); cerr.write(names, comma - names) << ": " << arg1 << " |"; __f(comma + 1, args...); }

#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif

void solve() {
	int n, m;
	cin >> n >> m;
	map<int, vector<int>> mp;
	for(int i=0; i<m; i++) {
		int x, y;
		cin >> x >> y;
		mp[x].push_back(y);
	}
	unordered_set<int> s;
	s.insert(n);
	for(auto&[_, b]: mp) {
		vector<int> add;
		for(auto y: b) {
			if(s.count(y-1) or s.count(y+1)) {
				add.push_back(y);
			}
		}
		for(auto d: b) {
			s.erase(d);
		}
		for(auto a: add) {
			s.insert(a);
		}
	}
	cout << s.size() << endl;
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	solve();
	return 0;
}


#include <bits/stdc++.h>
using namespace std;

// template {{{
#define  range(i, l, r) for (int i = (int)(l); i < (int)(r); (i) += 1)
#define rrange(i, l, r) for (int i = (int)(r) - 1; i >= (int)(l); (i) -= 1)

#define  whole(f, x, ...) ([&](decltype((x)) container) { return (f)(  begin(container),  end(container), ## __VA_ARGS__); })(x)
#define rwhole(f, x, ...) ([&](decltype((x)) container) { return (f)( rbegin(container), rend(container), ## __VA_ARGS__); })(x)

#define debug(x) cerr << "(" << __LINE__ << ")" << #x << ": " << (x) << endl

using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;

constexpr i32 mod   = 1e9 + 7;
// constexpr i32 mod   = 998244353;

constexpr i32 inf   = 1001001001;
constexpr i64 infll = 1001001001001001001ll;

constexpr i32 dx[] = {0, -1, 1, 0, -1, 1, -1, 1}; 
constexpr i32 dy[] = {-1, 0, 0, 1, -1, -1, 1, 1};

struct IoSetup { IoSetup(i32 x = 15){ cin.tie(0); ios::sync_with_stdio(0); cout << fixed << setprecision(x); cerr << fixed << setprecision(x); } } iosetup;

template <typename T = i64> T input() { T x; cin >> x; return x; }

template <typename T> ostream &operator<<(ostream &os, vector<T> &v) { range(i, 0, v.size()) { os << v[i] << (i + 1 != (int)v.size() ? " " : ""); } return os; } 
template <typename T> istream &operator>>(istream &is, vector<T> &v) { for (T &in : v) is >> in; return is; }

template <typename T1, typename T2> ostream &operator<<(ostream &os, pair<T1, T2> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
template <typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { is >> p.first >> p.second; return is; }

template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
// }}}

void solve() {
  int n, m;
  cin >> n >> m;

  vector< int > cnt(10000, 0);
  range(i, 0, n + m) {
    int a = input();
    cnt[a]++;
  }

  vector< int > ans;
  range(k, 0, cnt.size()) {
    if (cnt[k] == 1) {
      ans.emplace_back(k);
    }
  }

  cout << ans << endl;
}

signed main() {
  solve();
}
