Here is my code:
int main()
{
    int N, K;
    cin >> N >> K;
    int connect = 1;
    int temp = N;
    int largepow = 0;
// calculate the largest power of 2 less than K
    while(temp > 0)
    {
        if(pow(2, largepow) < K && pow(2, largepow + 1) < K)
            largepow++;
        temp /= 2;
    }
    N--;
    int count = 0;
// count the hours
    while(N > 0)
    {
        N -= connect;
        count++;
        if(connect < pow(2, largepow))
            connect *= 2;
        else if(connect >= pow(2, largepow) && connect < K)
            connect++;
    }
    cout << count;
    return 0;
}

Got WA4, then I tried something else:

int main ()
{
    long long n, k, exp;
    cin >> n >> k;
    for (exp = 0; (1 << exp) < n && (1 << exp) < k; exp++)
        if ((1 << exp) < n)
            exp += ((n - (1 << exp) - 1) / k) + 1;
    cout << exp;
    return 0;
}
Test case 4 again. What is wrong?