题解

n年以前写的

#include <iostream>
using namespace std;

int main()
{
    int tree,moves;
    bool moved[10005]={false};
    cin >> tree >> moves;
    for (int i=1;i<=moves;i++){
        int l,r;
        cin >> l >> r;
        for (int j=l;j<=r;j++){
            moved[j]=true;
        }
    }
    int count = 0;
    for (int i=0;i<=tree;i++){
        if (!moved[i]){
            count++;
        }
    }
    cout << count;
    return 0;
}