#include <bits/stdc++.h>

using namespace std;


typedef int32_t h_int32;
typedef int64_t h_int64;
typedef uint32_t uh_int32;
typedef uint64_t uh_int64;
typedef h_int64 h_int;

#define REP( i, n ) for(h_int i = 0; i < ( h_int )( n ); ++i )
#define REPR( i, n ) for(h_int i = ( h_int )( n ); i >= 0; --i )
#define FOR( i, a, n ) for(h_int i = ( h_int )( a ); i < ( h_int )( n ); ++i )
#define FORR( i, a, n ) for(h_int i = ( h_int )( n ); i >= ( h_int )( a ); --i)

#define ALL( x ) x.begin(), x.end()

#define DOUT( x ) cerr << #x << " = " << x << "\n"
#define COUT( x ) cout << ( x ) << "\n"
#define DOUBLECOUT( num, x ) cout << fixed << setprecision( num ) << ( x ) << "\n"

#define INF 999999999
#define PI 3.14159265359

signed main()
{
        ios::sync_with_stdio( false );
        cin.tie( 0 );

        int n, k;
        cin >> n >> k;

        if( k == 0 || k > n)
        {
                COUT( 0 );
                return 0;
        }
        COUT( ( n - k + 1 == k ) ? n - 1 : n - 2 );
        return 0;
}