int f(int num, int a[], int n) {
    int r = n - 1, l = 0, z = abs(num - (a[r] + a[l]));
    int r_ans = r, l_ans = 0;
    while(r - l != 0) {
        int k = abs(num - (a[r] + a[l]));
        if(k < z) {
            z = k;
            r_ans = r;
            l_ans = l;
        }
        if (a[r] + a[l] > num) {
            r--;
        } else if (a[r] + a[l] < num) {
            l++;
        } else {
            break;
        }
    }
    return a[l_ans] + a[r_ans];
}