for (int i = 0; i < n; i++) {
    int t = grades[i];

    if (t >= 38) {
        int nextMulof5 = ((t / 5) + 1) * 5;     //Calculation for next mul of 5
        if ((nextMulof5 - t) < 3) {
            grades[i] = nextMulof5;
        }
    }
}