最优雅的解法

#include <bits/stdc++.h>
using namespace std;

bool bucket[10010];

int main() {
  int m, q;
  cin >> m >> q;
  while (q--) {
    int l, r;
    cin >> l >> r;
    memset(bucket + l, true, r - l + 1);
  }
  cout << count(bucket, bucket + m + 1, false);
  return 0;
}