#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
    int n, a;
    cin >> n >> a;

    if (n == 1)
        cout << 0 << endl;
    else
    {
        int S = n - 1;
        //int S = n;
        for (int i = 1; i <= n; i++)
        {
            S = S - min(a, i);

            if (S <= 0)
            {
                cout << i << endl;
                break;
            }
        }
    }
}