#include <iostream>

const int NMAX = 30;
const int MOD = 666013;

using namespace std;

int N,M;
bool used[NMAX];
int answer = 0;
int sol[NMAX];
int mat[NMAX];

void backt(int k, int NN)
{
    if (k == NN+1)
    {
        answer += 1;
    }
    for (int i = 1; i <= NN; ++i)
    {
        if (i != k && !used[i])
        {
            used[i] = true;
            sol[k] = i;
            backt(k + 1, NN);
            used[i] = false;
        }
    }
}

int main()
{
    cin >> N >> M;
    mat[1] = 0;
    for (int i = 2; i <= M; ++i)
    {
        mat[i] = i*mat[i-1];
        if (i % 2 == 0)
        {
            mat[i] += 1;
        }
        else
        {
            mat[i] -= 1;
        }
    }

    cout << mat[N];
}