#include <string.h>
#include <vector>
#include <queue>
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <algorithm>
#define MAXSIZE 1000010
using namespace std;
int doors[MAXSIZE];
int N, L, K;
int ans;
int bin_search(int key)
{
	int res = -1;
	int left = 0;
	int right = N-1;
	while(left <= right)
	{
		int mid = (left + right)/2;
		if(doors[mid] >= key)
		{
			res = mid;
			right = mid-1;
		}
		else
		{
			left = mid+1;
		}
	}
	return res;
}


int main()
{
	
	ifstream f_in;
    ofstream f_out;

    f_in.open("metro.in",ios::in);
    f_out.open("metro.out",ios::out);

    f_in >> L;
	f_in >> K;
	f_in >> N;

	memset(doors,0, sizeof(doors)/sizeof(int));

	for(int i = 0; i < N; i++)
	{
		f_in>>doors[i];
	}

	int result = bin_search(K);


	f_out<<K - result;
	f_out<<endl;
	return 0;
}<!-- 0.0404s -->