#include <bits/stdc++.h>
#define FOR(i,bg,ed) for(ll i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007
#define int long long
using namespace std;
typedef long long ll;
const int INF = 1e9;



signed main()
{
    int N, K;

    cin >> N >> K;
    int ans = 0;
    for (int i=0; i<(1<<N); i++) {
        if (i == 0 || i == (1 << N) - 1) continue;

        int minPos;
        for (minPos=0; minPos<N; minPos++) {
            if (~i >> minPos & 1) break;
        }
        if (minPos + 1 != K) continue;

        int maxPos;
        for (int j=0; j<N; j++) {
            if (~i >> j & 1) maxPos = j;
        }
        int minPos2;
        for (minPos2=0; minPos2<N; minPos2++) {
            if (i >> minPos2 & 1) break;
        }
        if (minPos2 < maxPos) ans++;
    }

    cout << ans << endl;
}