import java.util.Scanner;

public class Main {

	static Scanner scanner;
	public static void main(String[] args) {
	    scanner = new Scanner(System.in);

	    int N= gi();
	    int M= gi();
	    int[] L = new int[M];
	    int[] R = new int[M];


	    for (int i=0; i<M;i++) {
	    	L[i]=gi();
	    	R[i]=gi();
	    }

	    int minr=Integer.MAX_VALUE;
	    int maxl=0;

	    for (int i=0; i<M;i++) {
	    	if(maxl < L[i]) {
	    		maxl=L[i];
	    	}
	    	if(minr>R[i]) {
	    		minr=R[i];
	    	}
	    }


        System.out.print(Math.max(minr-maxl+1,0));
	}

	// 文字列として入力を取得
	public static String gs() {
		return scanner.next();
	}

	// intとして入力を取得
	public static int gi() {
		return Integer.parseInt(scanner.next());
	}

	// longとして入力を取得
	public static long gl() {
		return Long.parseLong(scanner.next());
	}
}
/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