import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		try (Scanner sc = new Scanner(System.in)) {
			int N, M;
			N = Integer.parseInt(sc.next());
			M = Integer.parseInt(sc.next());

			int iniMax = 0, endMin = N;

			for (int i = 0; i < M; i++) {
				int ini = Integer.parseInt(sc.next());
				int end = Integer.parseInt(sc.next());
				
				iniMax = Math.max(iniMax, ini);
				endMin = Math.min(endMin, end);
			}
			int ans = endMin - iniMax + 1;
			if (ans > 0) System.out.println(ans);
			else System.out.println("0");		}
		 catch (Exception e) {
			// TODO: handle exception
		}

	}

}

/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