70分求助，看来几遍自己找不出自己问题

#include <stdio.h>
int main()
{
    int arr[100000] = { 0 };
    int l = 0, n = 0;
    scanf("%d %d", &l, &n);
    for (int i = 0; i < l; i++)
    {
        arr[i] = i;
    }
    for (int j = 0; j < n; j++)
    {
        int a, s;
        scanf("%d %d", &a, &s);
        for (a; a <= s; a++)
        {
            if (arr[a] != 0)
            {
                arr[a] = 0;
                l--;
            }
        }
        a = 0;
        s = 0;
    }
    printf("%d", l+1);
    return 0;
}