include
using namespace std;
int main() {
int l, m;
cin >> l >> m;
int* begin = new int[m];
int* end = new int[m];
// 从0开始输入数据
for (int i = 0; i < m; i++) {
cin >> begin[i] >> end[i];
}
int* q = new int[l];//定义一个长度为L的数组;
for (int i = 0; i < l; i++) {
q[i] = 0;
}
// 使用正确的循环变量和索引范围
for (int i = 0; i < m; i++) {
for (int j = begin[i] - 1; j < end[i]; j++) {
q[j] = 1;
}
}
int count = 0;
for (int i = 0; i < l; i++) {
if (q[i] == 0) {
count++;
}
}
cout << count+1;
delete[] begin;
delete[] end;
delete[] q;
return 0;
}

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