#include<iostream>

#include<algorithm>

using namespace std;

#define ll long long

int num[] = { , , , , , , , , , , , , ,  };

int len = ;

int a, b, n;

int ans;

void DFS(int k, int n){

    if (k == ){ ++ans; return; }

    for (int i = n + ; num[i] - num[n] <= b&&i<len; ++i)

    if (num[i]-num[n]>=a)

        DFS(num[i], i);

}

int main(){

    cin >> a >> b;

    cin >> n;

    while (n--){

        int x;

        cin >> x;

        num[len++] = x;

    }

    sort(num, num + len);

    DFS(, );

    cout << ans << endl;

}