import java.util.Scanner;

public class Main{
    public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
	int N = sc.nextInt();
	int M = sc.nextInt();

	int L = 0;
	int R = 0;
	int Lmax = 0;
	int Rmin = N;
	for(int i=0;i<M;i++){
	    L = sc.nextInt();
	    R = sc.nextInt();
	    if(L > Lmax) Lmax=L;
	    if(R < Rmin) Rmin=R;
	}
	if(Lmax <= Rmin) System.out.print(Rmin -Lmax +1);
	else System.out.print(0);
    }
}

/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