#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

signed main(){
  vector< vector< ll > > C( 25, vector< ll >( 25 ) );
  C[ 0 ][ 0 ] = 1;
  for( int i = 0; i < 21; ++i )
    for( int j = 0; j < 21; ++j )
      C[ i + 1 ][ j ] += C[ i ][ j ],
      C[ i + 1 ][ j + 1 ] += C[ i ][ j ];
  int N, K; cin >> N >> K;
  ll ans = 0;
  for( int mid = 1; mid <= N; ++mid ) if( mid != K )
    for( int pos = 1; pos < N; ++pos ){
      if( pos == 1 and K < mid ) continue;
      int ng = 0;
      for( int i = 1; i <= N; ++i ) if( i != K and i != mid )
        ng |= i < min( K, mid );
      if( ng ) continue;
      int less = 0;
      for( int i = 1; i <= N; ++i ) if( i != K and i != mid )
        less += i < max( K, mid );
      int a = N - 2 - less;
      int b = pos - 1;
      ans += C[ a ][ b ];
    }
  cout << ans << endl;
  return 0;
}