#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
const int FFTMOD = 1007681537;
const int INF = (int)1e9;
const long long LINF = (long long)1e18;
const long double PI = acos((long double)-1);
const long double EPS = 1e-9;
inline long long gcd(long long a, long long b) {
  long long r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
inline long long fpow(long long n, long long k, int p = MOD) {
  long long r = 1;
  for (; k; k >>= 1) {
    if (k & 1) r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T>
inline int chkmin(T& a, const T& val) {
  return val < a ? a = val, 1 : 0;
}
template <class T>
inline int chkmax(T& a, const T& val) {
  return a < val ? a = val, 1 : 0;
}
inline long long isqrt(long long k) {
  long long r = sqrt(k) + 1;
  while (r * r > k) r--;
  return r;
}
inline long long icbrt(long long k) {
  long long r = cbrt(k) + 1;
  while (r * r * r > k) r--;
  return r;
}
inline void addmod(int& a, int val, int p = MOD) {
  if ((a = (a + val)) >= p) a -= p;
}
inline void submod(int& a, int val, int p = MOD) {
  if ((a = (a - val)) < 0) a += p;
}
inline int mult(int a, int b, int p = MOD) { return (long long)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(long double x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(long double x, long double y) { return sign(x - y); }
long long f[10];
void solve() {
  int n, k;
  cin >> n >> k;
  f[0] = 1;
  f[2] = n * (n - 1) / 2;
  int perm[4] = {0, 1, 2, 3};
  int tot = 0;
  do {
    int found = 0;
    for (int i = (0); i < (4); i++)
      if (perm[i] == i) {
        found = 1;
      }
    tot += !found;
  } while (next_permutation(perm, perm + 4));
  f[4] = (long long)n * (n - 1) * (n - 2) * (n - 3) / 1 / 2 / 3 / 4 * tot;
  tot = 0;
  do {
    int found = 0;
    for (int i = (0); i < (3); i++)
      if (perm[i] == i) {
        found = 1;
      }
    tot += !found;
  } while (next_permutation(perm, perm + 3));
  f[3] = (long long)n * (n - 1) * (n - 2) / 1 / 2 / 3 * tot;
  long long res = 0;
  for (int i = (0); i < (k + 1); i++) {
    res += f[i];
  }
  cout << res << "\n";
}
int main(int argc, char* argv[]) {
  ios_base::sync_with_stdio(0), cin.tie(0);
  if (argc > 1) {
    assert(freopen(argv[1], "r", stdin));
  }
  if (argc > 2) {
    assert(freopen(argv[2], "wb", stdout));
  }
  solve();
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}
