0分求助，例子和下载的样例一都对，但就是一个不过

#include <iostream>

using namespace std;


int main() {
	int n, times, count;

	cin >> n >> times;
	int arr[n + 1] = {0};


	for (int i = 0; i < times; i++) {
		int a = 0;
		int b = 0;
		cin >> a >> b;
		for (int j = a; j <= b; j++) {
			arr[j] = 1;
		}
	}

	for (int i = 0; i < n + 1; i++) {
		if (arr[i] == 0)
			count++;
	}
	cout << count;

}