#include<stdio.h>
int main() {
	int l, m, u, v, sum = 0, i, x[10000] = {0}, max = 0, j;
	scanf("%d %d", &l, &m);
	for (i = 0; i < m; i++) {
		scanf("%d %d", &u, &v);
		for (j = u; j <= v; j++)
			x[j] = 1;
	}
	for (i = 0; i <= l; i++)
		if (x[i] == 1)
			sum++;
	printf("%d", l+1-sum);
	return 0;
	
}