#include <cstdio>
#include <algorithm>
#pragma warning(disable : 4996)
using namespace std;
int N, M, x, d, p;
int main() {
	scanf("%d %d", &N, &M);
	int al = N, ar = -1, bl = N, br = -1;
	for (int i = 0; i < M; i++) {
		scanf("%d %d", &x, &d);
		for (int j = 0; j < d; j++) {
			scanf("%d", &p);
			if (x > p) {
				al = min(al, p);
				ar = max(ar, x);
			}
			if(x < p) {
				bl = min(bl, x);
				br = max(br, p);
			}
		}
	}
	if (ar == -1 && br == -1) printf("0\n");
	else if (ar == -1) printf("%d\n", br - bl);
	else if (br == -1) printf("%d\n", ar - al);
	else printf("%d\n", min(ar + br - 2 * min(al, bl), 2 * max(ar, br) - al - bl));
	return 0;
}