#include <stdio.h>

int road[10005];
int main() {
	int l, m, ans = 1;
	
	int u, v;
	scanf("%d %d", &l, &m);
	for ( int i = 0; i < m; i++) {

		scanf("%d %d", &u, &v);
		for ( int j = u; j <= v; j++)
			road[j] = 1;
	}
	for (int i = 0; i < l; i++)
		if (road[i] == 0)
			ans++;
	printf("%d", ans);
	return 0;
}