#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <bits/stdc++.h>
using namespace std;
using i32 = int32_t;  using i64 = int64_t;  using str = string;
using u32 = uint32_t; using u64 = uint64_t; using usize = size_t;
using f64 = double_t; template <typename T> using vec = vector<T>;
#define times(n, i) for (i64 i = 0; i < (n); ++i)
#define range(n, m, i) for (i64 i = (n); i < (m); ++i)
#define upto(n, m, i) for (i64 i = (n); i <= (m); ++i)
#define downto(n, m, i) for (i64 i = (n); i >= (m); --i)
#define foreach(xs, x) for (auto &x : (xs))
#define all(xs) (xs).begin(), (xs).end()
#define sortall(xs) sort(all(xs))
#define reverseall(xs) reverse(all(xs))
#define uniqueall(xs) (xs).erase(unique(all(xs)), (xs).end())
#define maximum(xs) (*max_element(all(xs)))
#define minimum(xs) (*min_element(all(xs)))
#define even(x) (((x) & 1) == 0)
#define odd(x) (((x) & 1) == 1)
#define append emplace_back
const i64 MOD = 1000000007;

i32 n, k;
i64 fact[21];

i64 comb(i32 a, i32 b) {
    if (a < 1 || b < 1 || a == b)
        return 1;
    return fact[a]/fact[a-b]/fact[b];
}

i32 main()
{
    cin >> n >> k;
    
    fact[1] = 1;
    upto(2, 20, i) {
        fact[i] = fact[i-1] * i;
    }

    i64 ans = 0;
    upto(0, n-k, i) {
        ans += comb(n-k, i);
    }
    if (k == 1)
        ans -= n-k+1;
    
    cout << ans << endl;
    return 0;
}