import java.io.*;
import java.util.*;

public class Main {

	final static long MOD = 1000000007;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	}


	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


} import java.io.*; io.* java import java.util.*; util.* java public class Main {

	final static long MOD = 1000000007;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	}


	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


} Main final static long MOD = 1000000007; MOD 1000000007 public static String[] Ws = null; Ws null public static int wsIndx = 0; wsIndx 0 public static BufferedReader in = null; in null public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	} main {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	} int N=nextInt(); N nextInt() nextInt int M=nextInt(); M nextInt() nextInt int[] G = new int[N+1]; G new int[N+1] N+1 N 1 Arrays.fill(G, 0) Arrays.fill Arrays G 0 for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		} int i=0; int i=0; i 0 i<M i M i++ i++ i {
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		} {
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		} int[] p = nextInts(); p nextInts() nextInts G[p[0]-1]++ G[p[0]-1] G p[0]-1 p[0] p 0 1 G[p[1]]-- G[p[1]] G p[1] p 1 for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			G[i+1]+=G[i];
		} {
			G[i+1]+=G[i];
		} G[i+1]+=G[i] G[i+1] G i+1 i 1 G[i] G i long ans = 0; ans 0 for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			if(G[i]==M)
				ans++;
		} {
			if(G[i]==M)
				ans++;
		} if(G[i]==M)
				ans++; G[i]==M G[i] G i M ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	} check {
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	} if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		} in == null in null {
			in = new BufferedReader(new InputStreamReader(System.in));
		} in = new BufferedReader(new InputStreamReader(System.in)) in new BufferedReader(new InputStreamReader(System.in)) if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		} Ws==null || Ws.length<=wsIndx Ws==null Ws null Ws.length<=wsIndx Ws.length Ws Ws.length wsIndx {
			Ws = in.readLine().split(" ");
			wsIndx=0;
		} Ws = in.readLine().split(" ") Ws in.readLine().split(" ") in.readLine().split in.readLine() in.readLine in " " wsIndx=0 wsIndx 0 public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	} nextInt {
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	} check() check return Integer.parseInt(Ws[wsIndx++]); Integer.parseInt(Ws[wsIndx++]) Integer.parseInt Integer Ws[wsIndx++] Ws wsIndx++ wsIndx public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	} nextLong {
		check();
		return Long.parseLong(Ws[wsIndx++]);
	} check() check return Long.parseLong(Ws[wsIndx++]); Long.parseLong(Ws[wsIndx++]) Long.parseLong Long Ws[wsIndx++] Ws wsIndx++ wsIndx public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	} nextString {
		check();
		return Ws[wsIndx++];
	} check() check return Ws[wsIndx++]; Ws[wsIndx++] Ws wsIndx++ wsIndx public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	} nextInts {
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	} check() check int[] tmp = new int[Ws.length]; tmp new int[Ws.length] Ws.length Ws Ws.length for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		} int i=0; int i=0; i 0 i<tmp.length i tmp.length tmp tmp.length i++ i++ i {
			tmp[i]=Integer.parseInt(Ws[i]);
		} {
			tmp[i]=Integer.parseInt(Ws[i]);
		} tmp[i]=Integer.parseInt(Ws[i]) tmp[i] tmp i Integer.parseInt(Ws[i]) Integer.parseInt Integer Ws[i] Ws i wsIndx=Ws.length wsIndx Ws.length Ws Ws.length return tmp; tmp public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	} nextLongs {
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	} check() check long[] tmp = new long[Ws.length]; tmp new long[Ws.length] Ws.length Ws Ws.length for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		} int i=0; int i=0; i 0 i<tmp.length i tmp.length tmp tmp.length i++ i++ i {
			tmp[i]=Long.parseLong(Ws[i]);
		} {
			tmp[i]=Long.parseLong(Ws[i]);
		} tmp[i]=Long.parseLong(Ws[i]) tmp[i] tmp i Long.parseLong(Ws[i]) Long.parseLong Long Ws[i] Ws i wsIndx=Ws.length wsIndx Ws.length Ws Ws.length return tmp; tmp public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	} nextStrings {
		check();
		wsIndx=Ws.length;
		return Ws;
	} check() check wsIndx=Ws.length wsIndx Ws.length Ws Ws.length return Ws; Ws public class Main {

	final static long MOD = 1000000007;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	}


	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


} public class Main {

	final static long MOD = 1000000007;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	}


	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


} Main
import java.io.*;
import java.util.*;

public class Main {

	final static long MOD = 1000000007;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static void main(String[] args) throws Exception {

		int N=nextInt();
		int M=nextInt();

		int[] G = new int[N+1];
		Arrays.fill(G, 0);
		for(int i=0;i<M;i++){
			int[] p = nextInts();
			G[p[0]-1]++;
			G[p[1]]--;
		}

		for(int i=0;i<N;i++){
			G[i+1]+=G[i];
		}
		long ans = 0;
		for(int i=0;i<N;i++){
			if(G[i]==M)
				ans++;
		}
		System.out.println(ans);
	}


	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


}
