import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	}
	static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task
	
	
	static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.OutputStream; OutputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	}
	static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task
	
	
	static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	}
} Main public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	} main {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	} InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) Task solver = new Task(); solver new Task() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task Task public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve solve {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		} int n = in.nextInt() n in.nextInt() in.nextInt in m = in.nextInt(); m in.nextInt() in.nextInt in int se = 100002 se 100002 fi = 0; fi 0 for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			} int t = -1; int t = -1; t -1 1 ++t < m ++t t m {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			} {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			} fi = Math.max(fi, in.nextInt()) fi Math.max(fi, in.nextInt()) Math.max Math fi in.nextInt() in.nextInt in se = Math.min(se, in.nextInt()) se Math.min(se, in.nextInt()) Math.min Math se in.nextInt() in.nextInt in out.print(Math.max(0, se-fi+1)) out.print out Math.max(0, se-fi+1) Math.max Math 0 se-fi+1 se-fi se fi 1 int testNumber testNumber InputReader in in PrintWriter out out static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	} InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		} InputReader {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		} reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		} next {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		} while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			} tokenizer == null || ! tokenizer.hasMoreTokens() tokenizer == null tokenizer null ! tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			} try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				} catch (IOException e) {
					throw new RuntimeException(e);
				} IOException e {
					throw new RuntimeException(e);
				} throw new RuntimeException(e); new RuntimeException(e) {
					tokenizer = new StringTokenizer(reader.readLine());
				} tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		} nextIntArray {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		} int[] a = new int[n]; a new int[n] n for(int i = -1; ++i < n;) a[i] = nextInt(); int i = -1; int i = -1; i -1 1 ++i < n ++i i n a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long nextLong() {
			return Long.parseLong(next());
		} nextLong {
			return Long.parseLong(next());
		} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	}
	static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task
	
	
	static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	}
} public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	}
	static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task
	
	
	static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	}
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();

	}
	static class Task{
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			int n = in.nextInt(), m = in.nextInt();
			int se = 100002, fi = 0;
			for(int t = -1; ++t < m;) {
				fi = Math.max(fi, in.nextInt());
				se = Math.min(se, in.nextInt());
				
			}
			out.print(Math.max(0, se-fi+1));
		}//Solve
	}//task
	
	
	static class InputReader{
		public BufferedReader reader;
		public StringTokenizer tokenizer;
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
		public String next() {
			while(tokenizer == null || ! tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for(int i = -1; ++i < n;) a[i] = nextInt();
			return a;
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
	}
}
