#include<stdio.h>

int main() { int c,n; scanf("%d %d", &c, &n); int long_arr[c + 1]; for(int i=0;i<=c;i++){ long_arr[i]=1; } int a[n + 1], b[n + 1]; for (int i = 1; i <= n; i++) { scanf("%d %d", &a[i], &b[i]);

}
for (int i = 1; i <= n; i++) {
	for (int j = a[i]; j <= b[i]; j++) {
		if (long_arr[j] == 1) {
			long_arr[j] = 0;
		}
	}
}
int sum = 0;
for (int i = 0; i <= c; i++) {
	if (long_arr[i] == 1) {
		sum += 1;
	}
}
printf("%d", sum);
return 0;

}