import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String[] in = br.readLine().split(" ");
        int n = Integer.parseInt(in[0]);
        int m = Integer.parseInt(in[1]);

        int l0 = 0;
        int r0 = 1000000000;
        for(int i = 0; i < m; i++) {
            in = br.readLine().split(" ");
            int l = Integer.parseInt(in[0]);
            int r = Integer.parseInt(in[1]);
            l0 = Math.max(l0, l);
            r0 = Math.min(r0, r);
        }

        System.out.println(r0 >= l0? r0 - l0 + 1 : 0);

        br.close();
    }
}
/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