#include <bits/stdc++.h>
using namespace std;
int main () {
    int l, m, u, v, c = 0;
    cin >> l >> m;
    int a[l + 1];
    for (int i = 0; i <= l; i++) {
		a[i] = 1;
	}
    for (int i = 1; i <= m; i++) {
        cin >> u >> v;
        
    }for (int i = u; i <= v; i++){
            a[i] = 0;
    }
	for (int i = 0; i <= l; i++) {
        if (a[i] == 1) {
            c++;
        }
    }
    cout << c;
	return 0;
} 

为什么错了？求解答