int set_grade(struct student *p, int n) {
    int cnt = 0;

    for (int i = 0; i < n; i++) {
        if (p[i].score >= 85) {
            p[i].grade = 'A';
        } else if (p[i].score >= 70) {
            p[i].grade = 'B';
        } else if (p[i].score >= 60) {
            p[i].grade = 'C';
        } else {
            p[i].grade = 'D';
            cnt++;
        }
    }

    return cnt;
}