就例子对怎么改啊

#include<stdio.h>
int main() {
    int a[1000] = { 0 };
    int l,n;
    scanf("%d %d", &l,&n);
    int j, k,cnt=0;
    for (int x = 1; x <= n; x++) {
        scanf("%d %d", &j, &k);
        for (int p = j; p<= k; p++) {
            a[p] = -1;

        }

    }
    for (int i = 0; i <= l; i++) {
        if (a[i] != -1) cnt++;
    }
    printf("%d", cnt);
    return 0;
}