import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int M = Integer.parseInt(sc.next());
        int mi = N;
        int ma = 1;
        for(int i = 0;i < M;i++){
            int l = Integer.parseInt(sc.next());
            int r = Integer.parseInt(sc.next());
            if(ma < l){
                ma = l;
            }
            if(mi > r){
                mi = r;
            }
        }
        if(ma > mi){
            System.out.println(0);
        }else{
            System.out.println(mi-ma+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