import java.io.PrintStream;
import java.util.Arrays;
import java.util.Scanner;

/**
 * Solution to Breakout
 * 
 * @author vanb
 */
public class breakout_vanb
{
    /** Input. */
    private static Scanner sc;
    
    /** Output. */
    private static PrintStream ps;
    
    /**
     * Do it!
     */
    private void doit()
    { 
        int n = sc.nextInt();
        int x = sc.nextInt();
        int m = sc.nextInt();
        
        int circle[] = new int[n+1];
        Arrays.fill( circle, 0 );
        
        for( int i=0; i<m; i++ )
        {
            int crate = sc.nextInt();
            circle[crate]++;
        }
        
        int clock = 0;
        int room = 1;
        while( room!=x ) clock += circle[room++];
        
        int counter = 0;
        if( x>1 )
        {
            room = n;
            counter = circle[n];
            while( room!=x ) counter += circle[--room];
        }
    
        ps.println( Math.min( clock, counter ) );
    }
        
    /**
     * Main.
     * 
     * @param args unused
     * @throws Exception
     */
    public static void main( String[] args ) throws Exception
    {
        sc = new Scanner( System.in );
        ps = System.out;
        
        new breakout_vanb().doit();
    }

}