Using System;

class Program
{
    static int Comb(int K, int N, int T)
    {
        if (K == 2)
            return N + 1 - Math.Max(0, 2 * (N - T));
        
        int C = 0;
        for (int i = 0; i <= Math.Min(N, T); ++i)
            C += Comb(K - 1, N - i, T);
        
        return C;
    }
    
    static void Main(string[] args)
    {
        int N = Convert.ToInt32(Console.ReadLine());
        int T = Convert.ToInt32(Console.ReadLine()); // here input 1000
        
        Console.WriteLine(Comb(4, N, T));
       }
}