import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong(), M = sc.nextLong();
		List<Long> l = new ArrayList<>(), r = new ArrayList<>();
		for(int i = 0; i < M; i++) {
			l.add(sc.nextLong());
			r.add(sc.nextLong());
		}
		Collections.sort(l);
		Collections.sort(r);
		
		Long left = l.get(l.size()-1);
		Long right = r.get(0);
		
		Long ans = right-left+1;
		if(right >= left)System.out.println(ans);
		else System.out.println(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