import java.util.Scanner;

class Main {

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

	int N, M;
	N = sc.nextInt();
	M = sc.nextInt();

	int L[] = new int[M];
	int R[] = new int[M];
	for (int i = 0; i < M; i++) {
	    L[i] = sc.nextInt();
	    R[i] = sc.nextInt();
	}

	int l = L[0];
	int r = R[0];
	for (int i = 1; i < M; i++) {
	    if (l < L[i])
		l = L[i];
	    if (r > R[i])
		r = R[i];
	}

	if (r - l < 0)
	    System.out.println(0);
	else
	    System.out.println(r - l + 1);
    }
}
/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