import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		try (Scanner s = new Scanner(System.in)) {
			final int n = s.nextInt();
			final int m = s.nextInt();

			int maxStart = 0;
			int minEnd = n;

			for (int i = 0; i < m; i++) {
				int start = s.nextInt();
				int end = s.nextInt();
				if (start > maxStart) {
					maxStart = start;
				}
				if (end < minEnd) {
					minEnd = end;
				}
			}
			if (minEnd < maxStart) {
				System.out.println(0);
			} else {
				System.out.println(minEnd - maxStart + 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